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Stock Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Stock-Based Compensation (Details) [Line Items]      
Stock-based compensation expense $ 9,541 $ 6,559 $ 6,456
Stock-based compensation expense, tax benefit 1,715 2,117 2,464
Stock-based compensation expense, net of tax $ 7,826 $ 4,442 3,992
Vesting % of performance based restricted stock units, maximum 200.00%    
Restricted Stock Unit Activity (Table Details) [Abstract]      
Number of nonvested restricted stock units outstanding 867,755 635,573  
Granted 582,020    
Vested (56,421)    
Forfeited (293,417)    
Weighted average grant date fair value, outstanding $ 26.67 $ 28.53  
Weighted average grant date fair value, granted 27.85    
Weighted average grant date fair value, vested 35.78    
Weighted average grant date fair value, forfeited $ 31.29    
Stock Option Activity (Table Details) [Abstract]      
Number of awards outstanding 2,874,366 2,625,964  
Granted 717,265    
Exercised (65,366)    
Forfeited (254,447)    
Expired (149,050)    
Exercisable 1,325,966    
Weighted Average Exercise Price [Abstract]      
Equity awards outstanding $ 30.33 $ 30.63  
Granted 29.23    
Exercised 22.72    
Forfeited 31.10    
Expired 32.35    
Exercisable $ 30.18    
Weighted Average Remaining Contractual Life [Abstract]      
Equity awards outstanding 6 years 9 months 26 days    
Exercisable 5 years 22 days    
Aggregate Intrinsic Value [Abstract]      
Equity awards outstanding $ 17    
Exercisable 17    
Exercised 500 $ 1,900 5,800
Excess tax benefits related to stock awards $ 86 $ 331 $ 406
Assumptions Used in Fair Value Calculation of Stock Options (Table Details) [Abstract]      
Valuation method used Black-Scholes Black-Scholes Black-Scholes
Risk free interest rate, weighted average 1.42% 1.54% 0.88%
Expected dividend yield, maximum 3.32% 3.28% 2.34%
Expected life, weighted average 5 years 18 days 5 years 4 years 5 months 6 days
Expected volatility, weighted average 33.28% 34.77% 37.88%
Weighted average grant date fair value $ 6.34 $ 6.49 $ 9.27
Prior Plan [Member]      
Stock-Based Compensation (Details) [Line Items]      
Number of shares authorized to issue 14,562,865    
Stock Option Activity (Table Details) [Abstract]      
Number of awards outstanding 21,175 48,349  
Equity Incentive Plan [Member]      
Stock-Based Compensation (Details) [Line Items]      
Number of shares authorized to issue 2,468,461    
Stock Option Activity (Table Details) [Abstract]      
Number of awards outstanding 1,587,693 1,269,197  
2006 Plan [Member]      
Stock-Based Compensation (Details) [Line Items]      
Number of shares authorized to issue 7,000,000    
Stock Option Activity (Table Details) [Abstract]      
Number of awards outstanding 1,762,142 1,955,950  
Employee Stock Option [Member]      
Stock-Based Compensation (Details) [Line Items]      
Unvested awards - to result in compensation expense $ 6,900    
Weighted average number of years to vesting 2 years 6 months 26 days    
Stock-based compensation expense $ 4,030 $ 5,044 $ 3,944
Exercise period of options once vested 10 years    
Employee Stock Option [Member] | Minimum [Member]      
Stock-Based Compensation (Details) [Line Items]      
Vesting period of options granted 1 year    
Employee Stock Option [Member] | Maximum [Member]      
Stock-Based Compensation (Details) [Line Items]      
Vesting period of options granted 4 years    
Restricted Stock Units (RSUs) [Member]      
Stock-Based Compensation (Details) [Line Items]      
Unvested awards - to result in compensation expense $ 8,700    
Weighted average number of years to vesting 1 year 9 months 7 days    
Stock-based compensation expense $ 5,511 $ 1,515 $ 2,512
Restricted Stock Units (RSUs) [Member] | 2006 Plan [Member]      
Stock-Based Compensation (Details) [Line Items]      
Number of shares authorized to issue 3,500,000