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Stock-Based Compensation Plans (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock-based Compensation Plans (Textual) [Abstract]      
Stock-based compensation cost $ 18,900 $ 21,073 $ 18,851
Unrecognized compensation cost related to stock based compensation arrangements $ 34,700    
Weighted average period for recognition of cost 3 years 29 days    
Cash received from employee stock purchase plan purchases $ 7,100 7,100 7,200
Increase in financing activities and decrease in operating activities due to tax benefit relating to excess stock based compensation deductions   $ (249) $ 2,142
2014 Long Term Incentive Plan [Member]      
Stock-based Compensation Plans (Textual) [Abstract]      
Expiry date for stock options grant May 21, 2024    
Shares available for granted under the incentive plan 1,063,975    
Employee Stock Purchase Plan [Member]      
Stock-based Compensation Plans (Textual) [Abstract]      
Expiry date for stock options grant May 19, 2025    
Shares available for granted under the incentive plan 1,139,095    
Shares authorized under Employee stock option plan 4,500,000    
Employee stock purchase price in percentage of fair market value 85.00%    
Shares issued to employee under purchase plan 123,448 152,138 102,029
Weighted average fair value of employee stock purchase rights issued $ 16.51 $ 13.40 $ 18.56
Restricted Stock [Member]      
Stock-based Compensation Plans (Textual) [Abstract]      
Fair value of shares vested $ 19,200 $ 16,500 $ 13,900
Restricted Stock [Member] | Maximum [Member]      
Stock-based Compensation Plans (Textual) [Abstract]      
Range of forfeiture provisions 5 years