Stockholders' Equity - Summary of activity under Employee Stock Purchase Plan (Details) - Employee stock purchase plan - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period (in shares)	370,696	390,776	332,659	328,533
Granted (in shares)	0	0	212,716	235,572
Exercised (in shares)	(2,463)	(4,386)	(14,367)	(19,016)
Forfeited (in shares)	(6,514)	(23,172)	(29,495)	(39,797)
Expired (in shares)	0	0	(139,794)	(142,074)
Outstanding and exercisable, end of period (in shares)	361,719	363,218	361,719	363,218