Quarterly report pursuant to Section 13 or 15(d)

Non-Controlling Interest Non-Controlling Interest (Schedule of Equity) (Details)

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Non-Controlling Interest Non-Controlling Interest (Schedule of Equity) (Details) - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Noncontrolling Interest [Line Items]    
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification $ 14,100,000  
Common Stock, Dividends, Per Share, Cash Paid $ 0.22 $ 0.18
Balance, beginning of period $ 1,652,259,000 $ 1,581,511,000
Net income 48,729,000 38,885,000
Other comprehensive income (loss):    
Unrealized holding gains on available-for-sale securities 4,000 4,000
Derivative holding losses (4,907,000) (1,605,000)
Foreign currency translation adjustments 6,259,000 11,502,000
Cash dividends (15,452,000) (12,499,000)
Issuance of common stock under employee stock plans, net 5,347,000 4,278,000
Stock-based compensation expense 3,113,000 2,941,000
Stock Repurchased During Period, Value (18,099,000) (33,000,000)
Balance, end of period 1,691,353,000 $ 1,592,017,000
Parent [Member]    
Noncontrolling Interest [Line Items]    
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification $ 14,100,000  
Common Stock, Dividends, Per Share, Cash Paid $ 0.22 $ 0.18
Balance, beginning of period $ 1,621,951,000 $ 1,560,820,000
Net income 45,107,000 36,006,000
Other comprehensive income (loss):    
Unrealized holding gains on available-for-sale securities 4,000 4,000
Derivative holding losses (4,570,000) (1,527,000)
Foreign currency translation adjustments 5,019,000 11,248,000
Cash dividends (15,452,000) (12,499,000)
Issuance of common stock under employee stock plans, net 5,347,000 4,278,000
Stock-based compensation expense 3,113,000 2,941,000
Stock Repurchased During Period, Value (18,099,000) (33,000,000)
Balance, end of period 1,656,520,000 1,568,271,000
Non-controlling Interest [Member]    
Noncontrolling Interest [Line Items]    
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification 0  
Balance, beginning of period 30,308,000 20,691,000
Net income 3,622,000 2,879,000
Other comprehensive income (loss):    
Unrealized holding gains on available-for-sale securities 0 0
Derivative holding losses (337,000) (78,000)
Foreign currency translation adjustments 1,240,000 254,000
Cash dividends 0 0
Issuance of common stock under employee stock plans, net 0 0
Stock-based compensation expense 0 0
Stock Repurchased During Period, Value 0 0
Balance, end of period $ 34,833,000 $ 23,746,000