Net Income Per Share - Computation of Basic and Diluted Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to common stockholders	$ (5,888)	$ (2,896)	$ 7,409	$ 28,032	$ 69,254	$ 28,007	$ 18,346	$ 9,882	$ 26,657	$ 125,489	$ 75,129
Denominator:
Weighted average shares used to compute net income per share attributable to common stockholders, basic (in shares)									110,089	105,432	102,367
Weighted average effect of potentially dilutive shares to purchase common stock (in shares)									7,023	2,774	2,597
Weighted average shares used to compute net income per share attributable to common stockholders, diluted (in shares)									117,112	108,206	104,964
Net income per share attributable to common stockholders
Basic (in dollars per share)	$ (0.05)	$ (0.03)	$ 0.07	$ 0.26	$ 0.65	$ 0.26	$ 0.17	$ 0.09	$ 0.24	$ 1.19	$ 0.73
Diluted (in dollars per share)	$ (0.05)	$ (0.02)	$ 0.06	$ 0.25	$ 0.63	$ 0.26	$ 0.17	$ 0.09	$ 0.23	$ 1.16	$ 0.72