Stockholders' Equity - Outstanding and Reserved Shares of Common Stock for Future Issuance (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Common stock outstanding and reserved shares of common stock for future issuance
Options outstanding (in shares)	1,579,022	1,810,580
Total shares of common stock reserved for future issuance (in shares)	52,843,076
2012 Equity Incentive Plan
Common stock outstanding and reserved shares of common stock for future issuance
Total shares of common stock reserved for future issuance (in shares)	28,705,526
2012 Employee Stock Purchase Plan
Common stock outstanding and reserved shares of common stock for future issuance
Total shares of common stock reserved for future issuance (in shares)	10,396,547
Options outstanding
Common stock outstanding and reserved shares of common stock for future issuance
Options outstanding (in shares)	1,579,022
RSUs
Common stock outstanding and reserved shares of common stock for future issuance
RSUs (in shares)	12,161,981	10,201,660
Performance-based RSUs
Common stock outstanding and reserved shares of common stock for future issuance
Number of shares eligible to vest (percent)	100.00%