Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 135,311	$ 2	$ 538,901	$ 940	$ (404,532)
Beginning balance, Shares at Dec. 31, 2018		15,914,342
Issuance of common stock upon exercise of stock options	251		251
Issuance of common stock upon exercise of stock options, Shares		50,896
Release of restricted stock units		5,170
Stock-based compensation	3,703		3,703
Other comprehensive income (loss)	(449)			(449)
Net loss	(23,427)				(23,427)
Ending balance at Mar. 31, 2019	115,389	$ 2	542,855	491	(427,959)
Ending balance, Shares at Mar. 31, 2019		15,970,408
Beginning balance at Dec. 31, 2018	135,311	$ 2	538,901	940	(404,532)
Beginning balance, Shares at Dec. 31, 2018		15,914,342
Net loss	(62,957)
Ending balance at Sep. 30, 2019	82,046	$ 2	549,711	(178)	(467,489)
Ending balance, Shares at Sep. 30, 2019		16,102,889
Beginning balance at Mar. 31, 2019	115,389	$ 2	542,855	491	(427,959)
Beginning balance, Shares at Mar. 31, 2019		15,970,408
Issuance of common stock upon exercise of stock options	188		188
Issuance of common stock upon exercise of stock options, Shares		34,785
Issuance of common stock under Employee Stock Purchase Plan	164		164
Issuance of common stock under Employee Stock Purchase Plan, Shares		11,749
Release of restricted stock units		9,111
Stock-based compensation	3,336		3,336
Other comprehensive income (loss)	551			551
Net loss	(18,578)				(18,578)
Ending balance at Jun. 30, 2019	101,050	$ 2	546,543	1,042	(446,537)
Ending balance, Shares at Jun. 30, 2019		16,026,053
Issuance of common stock upon exercise of stock options	93		93
Issuance of common stock upon exercise of stock options, Shares		24,023
Release of restricted stock units		52,813
Stock-based compensation	3,075		3,075
Other comprehensive income (loss)	(1,220)			(1,220)
Net loss	(20,952)				(20,952)
Ending balance at Sep. 30, 2019	82,046	$ 2	549,711	(178)	(467,489)
Ending balance, Shares at Sep. 30, 2019		16,102,889
Beginning balance at Dec. 31, 2019	$ 65,595	$ 2	552,083	414	(486,904)
Beginning balance, Shares at Dec. 31, 2019	16,147,137	16,147,137
Issuance of common stock upon exercise of stock options	$ 80		80
Issuance of common stock upon exercise of stock options, Shares		17,691
Release of restricted stock units		2,585
Stock-based compensation	2,035		2,035
Other comprehensive income (loss)	(554)			(554)
Net loss	(7,575)				(7,575)
Ending balance at Mar. 31, 2020	59,581	$ 2	554,198	(140)	(494,479)
Ending balance, Shares at Mar. 31, 2020		16,167,413
Beginning balance at Dec. 31, 2019	$ 65,595	$ 2	552,083	414	(486,904)
Beginning balance, Shares at Dec. 31, 2019	16,147,137	16,147,137
Issuance of common stock upon exercise of stock options, Shares	21,295
Net loss	$ (38,730)
Ending balance at Sep. 30, 2020	$ 34,534	$ 2	558,920	1,246	(525,634)
Ending balance, Shares at Sep. 30, 2020	16,268,861	16,268,861
Beginning balance at Mar. 31, 2020	$ 59,581	$ 2	554,198	(140)	(494,479)
Beginning balance, Shares at Mar. 31, 2020		16,167,413
Issuance of common stock upon exercise of stock options	3		3
Issuance of common stock upon exercise of stock options, Shares		596
Issuance of common stock under Employee Stock Purchase Plan	40		40
Issuance of common stock under Employee Stock Purchase Plan, Shares		8,582
Release of restricted stock units		35,201
Stock-based compensation	3,028		3,028
Other comprehensive income (loss)	579			579
Net loss	(16,615)				(16,615)
Ending balance at Jun. 30, 2020	46,616	$ 2	557,269	439	(511,094)
Ending balance, Shares at Jun. 30, 2020		16,211,792
Issuance of common stock upon exercise of stock options	19		19
Issuance of common stock upon exercise of stock options, Shares		3,008
Release of restricted stock units		54,061
Stock-based compensation	1,632		1,632
Other comprehensive income (loss)	807			807
Net loss	(14,540)				(14,540)
Ending balance at Sep. 30, 2020	$ 34,534	$ 2	$ 558,920	$ 1,246	$ (525,634)
Ending balance, Shares at Sep. 30, 2020	16,268,861	16,268,861