Equity Plans - Employee Stock Options Valuation Assumptions (Details) - Employee stock options	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Plans
Expected volatility, Minimum	61.00%	62.00%	61.60%
Expected volatility, Maximum	64.80%	66.50%	65.40%
Risk-free interest rate, Minimum	1.42%	2.42%	1.88%
Risk-free interest rate, Maximum	2.58%	3.03%	2.24%
Minimum
Equity Plans
Expected term	5 years	5 years 5 months 27 days	5 years 6 months
Maximum
Equity Plans
Expected term	6 years 29 days	6 years 29 days	6 years 29 days