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Other Employee Benefits - Narrative (Details) - USD ($)
12 Months Ended
Jun. 13, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Jun. 20, 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of gross annual earnings (up to)   60.00%      
Percentage vested in salary reduction contributions   100.00%      
Shares of common stock         100,000
Discretionary contributions   $ 3,309,000 $ 3,270,000 $ 2,753,000  
ESPP          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Payroll deduction period (up to)   5 days      
Percentage of fair market value   85.00%      
Threshold amount of total amount of contributions   $ 21,000      
Threshold amount of common stock   $ 25,000      
Shares of common stock available   100,000      
Common stock available for issuance (in shares) 100,000