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Stock-Based Compensation - 401(k) Plan (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
401(k) Plan      
Summary of Company expenses attributable to the 401(k) Plan      
Expenses attributable to the 401(k) Plan $ 1,645,434 $ 1,356,035 $ 1,158,354