Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Narrative) (Details)

v3.10.0.1
Stock-Based Compensation (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options $ 7,900,000 $ 10,463,000 $ 9,576,000
Shares authorized 20,800,000    
Shares available for future grants 2,292,360    
Stock-based compensation expense $ 14,291,000 11,286,000 10,986,000
Stock Options [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Stock-based compensation expense 4,938,000 3,843,000 3,896,000
Unrecognized costs related to share based compensation $ 8,701,000    
Weighted average period of recognition of unrecognized costs related to stock options, years 2 years 2 months 20 days    
Intrinsic value of stock options exercised $ 22,388,000 19,836,000 12,976,000
Cash received on exercises of stock options $ 18,484,000 19,946,000 13,167,000
Stock Options [Member] | After2008 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 4 years    
Expiration period, years 10 years    
Service Based Restricted Stock Units [Member] | After2008 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 4 years    
Performance Based Restricted Stock Units [Member] | Minimum [Member] | Prior To2010 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 2 years 6 months    
Performance Based Restricted Stock Units [Member] | Minimum [Member] | After2009 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 2 years    
Performance Based Restricted Stock Units [Member] | Maximum [Member] | Prior To2010 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 3 years    
Performance Based Restricted Stock Units [Member] | Maximum [Member] | After2009 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 3 years    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Stock-based compensation expense $ 9,353,000 $ 7,443,000 $ 7,090,000
Unrecognized costs related to share based compensation $ 16,892,000    
Weighted average period of recognition of unrecognized costs related to stock options, years 2 years 2 months 10 days    
Company withheld shares 55,907 65,437 88,335
Company withheld shares, tax obligations $ 4,285,000 $ 3,662,000 $ 5,127,000
Grant date fair value of vested units $ 7,944,000 $ 7,477,000 $ 7,988,000