Equity Incentive Plans - Summary of Stock Option Activity Under 2008 Plan 2009 Plan and 2019 Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Subject to Outstanding Options, Options outstanding, Beginning Balance	15,157,930	12,089,694	12,919,342
Shares Subject to Outstanding Options, Options granted	4,194,491	4,764,625	1,604,496
Shares Subject to Outstanding Options, Options forfeited or cancelled	(412,357)	(929,519)	(2,207,933)
Shares Subject to Outstanding Options, Options exercised	(2,293,410)	(766,870)	(226,211)
Shares Subject to Outstanding Options, Options outstanding, Ending Balance	16,646,654	15,157,930	12,089,694
Shares Subject to Outstanding Options, Options vested and exercisable	10,101,496
Weighted Average Exercise Price per Share, Options outstanding, Beginning Balance	$ 4.52	$ 3.56	$ 3.28
Weighted Average Exercise Price per Share, Options granted	9.72	6.55	6.27
Weighted Average Exercise Price per Share, Options forfeited or cancelled	6.24	4.86	5.51
Weighted Average Exercise Price per Share, Options exercised	1.97	1.66	0.98
Weighted Average Exercise Price per Share, Options outstanding, Ending Balance	6.14	$ 4.52	$ 3.56
Weighted Average Exercise Price per Share, Options vested and exercisable	$ 4.58
Aggregate Intrinsic Value, Option outstanding	$ 398,379	$ 41,690	$ 36,165	$ 41,952
Aggregate Intrinsic Value, Options vested and exercisable	$ 255,939