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Stock Based Compensation - Summary of Restricted Stock Awards (Details) - Restricted Stock Awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Number of restricted stock, Unvested Beginning of period 1,366
Number of restricted stock, Forfeited (410)
Number of restricted stock, Vested (956)
Number of restricted stock, Unvested End of period
Weighted Average Grant Date Fair Value, Unvested Beginning of period $ 40.01
Weighted Average Grant Date Fair Value, Forfeited 44.84
Weighted Average Grant Date Fair Value, Vested 37.94
Weighted Average Grant Date Fair Value, Unvested End of period