Net Income Per Share - Anti-Dilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options and restricted stock not included in the calculation of diluted net income per share	7,677	88	0
Restricted stock subject to vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options and restricted stock not included in the calculation of diluted net income per share	31	88	0
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options and restricted stock not included in the calculation of diluted net income per share	3,823	0	0
Warrants related to the issuance of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options and restricted stock not included in the calculation of diluted net income per share	3,823	0	0