Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended					3 Months Ended		9 Months Ended
	Aug. 31, 2019	Feb. 28, 2019	Aug. 31, 2018	Jul. 31, 2018	Feb. 28, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from stock option exercised								$ 21,000
Proceeds						$ 200,000	$ 193,000	$ 397,000	$ 492,000
Issuance of common stock for services, shares						0	0	113,136	75,183
Issuance of common stock for services, amount						$ 300,000	$ 300,000	$ 311,000	$ 304,000
Stock based compensation expenses						$ 3,879,000	$ 1,948,000	$ 7,724,000	$ 6,976,000
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options exercised						4,513	0	6,964	0
Net proceeds from stock option exercised						$ 13,000	$ 0	$ 21,000	$ 0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued upon vesting of restricted stock units						0	0	85,609	0
Performance-Based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Granted				903,374
Number of Shares, Outstanding						850,309		850,309
Number of shares issued upon vesting of restricted stock units						0	0	0	0
Stock based compensation expenses						$ 2,100,000	$ 0	$ 2,100,000	$ 0
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued under ESPP	77,698	83,046	52,370		68,589
Purchase price	$ 2.58	$ 2.39	$ 3.66		$ 4.38
Proceeds	$ 200,000	$ 200,000	$ 200,000		$ 300,000