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Stock Incentive Programs - Additional Information (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Plan
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2014
shares
Feb. 22, 2012
shares
Dec. 31, 2004
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of Stock-Based Employee Compensation Plans | Plan 2          
Number of Stock-Based Employee Compensation Plans Expired | Plan 1          
Allocated share-based compensation expense | $ $ 6,900 $ 9,500 $ 11,100      
Income tax benefit recorded for stock-based compensation expense | $ $ 2,400 $ 3,300 $ 3,900      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 0 0 0      
Number of shares outstanding 0 5,000 29,000 53,000    
Total intrinsic value of options exercised | $ $ 202 $ 931        
Number of options vested 0          
Number of unvested options forfeited 0 0        
Proceeds from stock option exercises | $ $ 148 $ 778 $ 290      
Tax benefit realized from exercises of stock-based compensation arrangements | $ 0 0 0      
Total unrecognized compensation expense related to stock-based compensation arrangements | $ $ 28,800          
Weighted-average period of cost expected to be recognized 1 year 11 months 8 days          
Restricted Stock [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Allocated share-based compensation expense | $ $ 6,900 $ 9,500 $ 11,100      
Other than options granted 21,000          
Total fair value of options vested | $ $ 5,400          
Restricted Stock [Member] | Minimum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period 1 year          
Restricted Stock [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period 5 years          
Employee Stock Option [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting period 10 years          
2004 Stock Incentive Plan [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized           1,250,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 191,625          
Number of shares outstanding 0          
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 0          
2004 Stock Incentive Plan [Member] | Restricted Stock [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Other than options granted 793,218          
2012 Stock Incentive Plan [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized         1,250,000  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 359,133