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Net Income (Loss) Per Share - Additional Information (Details) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
RSU Vesting [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Unvested RSUs 1,373,457 933,727 599,234