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Stock Award Plans, All Plans Options and Restricted Stock Award Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Plans Combined Disclosure [Abstract]      
Intrinsic value of stock options exercised $ 6,709 $ 1,671 $ 266
Tax benefit from stock options exercised 2,073 632 100
Intrinsic value of restricted stock vesting 12,936 8,485 6,928
Tax benefit from restricted stock vesting 3,997 3,208 2,598
Fair value of options vested 3,191 2,530 2,495
Fair value of restricted stock vested $ 12,936 $ 8,485 $ 6,928
Fair value of stock options granted (in dollars per share) $ 23.53 $ 20.72 $ 17.30
Fair value of stock options granted $ 2,787 $ 2,617 $ 3,231
Stock Options [Member]      
Share-based Compensation Plans Combined Disclosure [Abstract]      
Unrecognized compensation cost related to unvested awards $ 2,294    
Weighted average period of recognition in years 1 year 6 months    
Fair Value Assumptions [Abstract]      
Dividend yield 0.00% 0.00% 0.00%
Average risk-free interest rate 2.70% 2.00% 1.50%
Stock price volatility 27.00% 27.00% 30.00%
Estimated option term 6 years 6 years 6 years
Restricted Stock [Member]      
Share-based Compensation Plans Combined Disclosure [Abstract]      
Unrecognized compensation cost related to unvested awards $ 8,647    
Weighted average period of recognition in years 2 years 2 months 12 days    
RSUs [Member]      
Share-based Compensation Plans Combined Disclosure [Abstract]      
Vesting (in shares) 0    
Unrecognized compensation cost related to unvested awards $ 5,732    
Weighted average period of recognition in years 3 years 10 months 24 days