Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Narrative) (Details)

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Stock-Based Compensation (Narrative) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
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 $ 9,900,000 $ 7,900,000 $ 10,500,000
Shares authorized 20,800,000    
Shares available for future grants 1,877,407    
Stock-based compensation expense $ 17,832,000 14,291,000 11,286,000
Stock Options [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Stock-based compensation expense 6,200,000 4,900,000 3,800,000
Unrecognized costs related to share based compensation $ 10,100,000    
Weighted average period of recognition of unrecognized costs related to stock options, years 2 years 1 month 24 days    
Vesting period of options granted, years 4 years    
Expiration period, years 10 years    
Intrinsic value of stock options exercised $ 26,800,000 22,400,000 19,800,000
Cash received on exercises of stock options 19,800,000 18,500,000 19,900,000
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Stock-based compensation expense 11,600,000 $ 9,400,000 $ 7,400,000
Unrecognized costs related to share based compensation $ 19,400,000    
Weighted average period of recognition of unrecognized costs related to stock options, years 2 years 21 days    
Company withheld shares 56,843 55,907 65,437
Company withheld shares, tax obligations $ 5,800,000 $ 4,300,000 $ 3,700,000
Grant date fair value of vested units $ 9,900,000 $ 7,900,000 $ 7,500,000
Vesting period of options granted, years 4 years    
Restricted Stock Units (RSUs) [Member] | Minimum | After2009 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 2 years    
Restricted Stock Units (RSUs) [Member] | Maximum | After2009 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Vesting period of options granted, years 3 years