Net Income Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income attributable to common stockholders - basic									$ 19,224	$ 15,865	$ 30,244
Denominator:
Weighted-average shares used in computing net income per share - basic									35,247	34,050	32,979
Effect of potentially dilutive securities:
Common stock options (in shares)									3,052	4,134	4,191
RSUs (in shares)					0				70		0
Weighted - average shares used in computing net income (loss) per share attributable to common stockholders - diluted (in shares)									38,369	38,184	37,170
Basic (usd per share)	$ 0.17	$ 0.14	$ 0.10	$ 0.14	$ 0.16	$ 0.12	$ 0.10	$ 0.09	$ 0.55	$ 0.47	$ 0.92
Diluted (usd per share)	$ 0.15	$ 0.13	$ 0.09	$ 0.13	$ 0.14	$ 0.11	$ 0.09	$ 0.08	$ 0.50	$ 0.42	$ 0.81
Stock Options
Antidilutive Securities
Common stock options (in shares)									3,241	1,582	1,689
RSUs
Antidilutive Securities
Common stock options (in shares)									24	0	0