Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Anti-dilutive securities
Anti-dilutive securities excluded from computation of earnings per share	3,835	4,992	4,005	6,104
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from computation of earnings per share	3,602	4,781	3,636	5,707
RSU
Anti-dilutive securities
Anti-dilutive securities excluded from computation of earnings per share	232	196	364	355
ESPP
Anti-dilutive securities
Anti-dilutive securities excluded from computation of earnings per share	1	15	5	42