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Stock-Based Compensation - Summary of Vested and Unvested Restricted Stock Units Outstanding (Details) - Restricted Stock Units (RSUs) - $ / shares
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Restricted Stock Units Outstanding, Balance, beginning of period (unvested) 1,214,325 1,200,848
Restricted Stock Units Outstanding, Grants 110,466 97,893
Restricted Stock Units Outstanding, Released and distributed (vested) (181,903) (70,819)
Restricted Stock Units Outstanding, Forfeited/expired (7,060) (1,021)
Restricted Stock Units Outstanding, Balance, end of period (unvested) 1,135,828 1,226,901
Weighted Average Grant Date Fair Value, Balance, beginning of period (unvested) $ 19.97 $ 19.00
Weighted Average Grant Date Fair Value, Grants 40.02 33.88
Weighted Average Grant Date Fair Value, Released and distributed (vested) 22.09 19.00
Weighted Average Grant Date Fair Value, Forfeited/expired 21.81 19.00
Weighted Average Grant Date Fair Value, Balance, end of period (unvested) $ 21.59 $ 19.67