Annual report pursuant to Section 13 and 15(d)

Fair Value Measures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details)

v3.3.1.900
Fair Value Measures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure $ 192,378 $ 232,634
Liabilities, Fair Value Disclosure 1,917 924
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 185,090 145,823
Liabilities, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 7,288 86,811
Liabilities, Fair Value Disclosure 1,917 924
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Liabilities, Fair Value Disclosure 0 0
Money Market Funds [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 114,247 94,112
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 114,247 94,112
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Bank Time Deposits [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 63,327 45,187
Bank Time Deposits [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 63,327 45,187
Bank Time Deposits [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Bank Time Deposits [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Certificates of Deposit [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   1,470
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   1,470
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Repurchase Agreements [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   40,000
Repurchase Agreements [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Repurchase Agreements [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   40,000
Repurchase Agreements [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
U.S. Government-Backed Municipal Bonds [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   5,812
U.S. Government-Backed Municipal Bonds [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   23,598
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   5,812
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   23,598
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
U.S. Government-Backed Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Short-term municipal bond fund [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   3,184
Short-term municipal bond fund [Member] | Fair Value, Inputs, Level 1 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Short-term municipal bond fund [Member] | Fair Value, Inputs, Level 2 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   3,184
Short-term municipal bond fund [Member] | Fair Value, Inputs, Level 3 [Member] | Available-for-sale Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure   0
Derivative Financial Instruments, Assets [Member] | Other Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 6,722 12,747
Derivative Financial Instruments, Assets [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 566  
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Other Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0  
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Other Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 6,722 12,747
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 566  
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Other Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0  
Mutual Fund Shares [Member] | Trading Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 629 485
Mutual Fund Shares [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 6,887 6,039
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 1 [Member] | Trading Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 629 485
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 1 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 6,887 6,039
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 2 [Member] | Trading Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 2 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 3 [Member] | Trading Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Mutual Fund Shares [Member] | Fair Value, Inputs, Level 3 [Member] | Non Current Assets [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, Fair Value Disclosure 0 0
Derivative Financial Instruments, Liabilities [Member] | Accrued Liabilities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Liabilities, Fair Value Disclosure 1,917 924
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member] | Accrued Liabilities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Liabilities, Fair Value Disclosure 0 0
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Liabilities, Fair Value Disclosure 1,917 924
Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Accrued Liabilities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Liabilities, Fair Value Disclosure $ 0 $ 0