CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional Paid-In Capital	Accumulated other comprehensive income (loss)	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2018	$ 14	$ 617,781	$ 1	$ (440,483)	$ 177,313
Beginning balances (in shares) at Dec. 31, 2018	143,870
Net income (loss)				663	663
Stock-based compensation expense		6,807			6,807
Issuance of common stock upon exercise of stock options		1,313			1,313
Issuance of common stock upon exercise of stock options (in shares)	468
Taxes paid related to net share settlement of equity awards	$ 1	(3,957)			(3,956)
Taxes paid related to net share settlement of equity awards (in shares)	560
Issuance of common stock pursuant to Employee Stock Purchase Plan		1,665			1,665
Issuance of common stock pursuant to Employee Stock Purchase Plan (in shares)	278
Other comprehensive income (loss)			15		15
Ending balance at Mar. 31, 2019	$ 15	623,609	16	(439,820)	183,820
Ending balances (in shares) at Mar. 31, 2019	145,176
Beginning balance at Dec. 31, 2018	$ 14	617,781	1	(440,483)	177,313
Beginning balances (in shares) at Dec. 31, 2018	143,870
Net income (loss)					3,170
Other comprehensive income (loss)					(15)
Ending balance at Jun. 30, 2019	$ 15	623,652	(14)	(437,313)	186,340
Ending balances (in shares) at Jun. 30, 2019	145,784
Beginning balance at Mar. 31, 2019	$ 15	623,609	16	(439,820)	183,820
Beginning balances (in shares) at Mar. 31, 2019	145,176
Net income (loss)				2,507	2,507
Stock-based compensation expense		2,035			2,035
Issuance of common stock upon exercise of stock options		469			469
Issuance of common stock upon exercise of stock options (in shares)	209
Taxes paid related to net share settlement of equity awards		(2,461)			(2,461)
Taxes paid related to net share settlement of equity awards (in shares)	399
Other comprehensive income (loss)			(30)		(30)
Ending balance at Jun. 30, 2019	$ 15	623,652	(14)	(437,313)	186,340
Ending balances (in shares) at Jun. 30, 2019	145,784
Beginning balance at Dec. 31, 2019	$ 15	634,721	(37)	(431,612)	203,087
Beginning balances (in shares) at Dec. 31, 2019	147,778
Net income (loss)				(8,273)	(8,273)
Stock-based compensation expense		6,238			6,238
Issuance of common stock upon exercise of stock options		9,526			9,526
Issuance of common stock upon exercise of stock options (in shares)	2,921
Issuance of common stock upon exercise of warrants (in shares)	115
Taxes paid related to net share settlement of equity awards		(1,720)			(1,720)
Taxes paid related to net share settlement of equity awards (in shares)	320
Issuance of common stock pursuant to Employee Stock Purchase Plan		1,705			1,705
Issuance of common stock pursuant to Employee Stock Purchase Plan (in shares)	450
Other comprehensive income (loss)			(23)		(23)
Ending balance at Mar. 31, 2020	$ 15	650,470	(60)	(439,885)	210,540
Ending balances (in shares) at Mar. 31, 2020	151,584
Beginning balance at Dec. 31, 2019	$ 15	634,721	(37)	(431,612)	203,087
Beginning balances (in shares) at Dec. 31, 2019	147,778
Net income (loss)					(16,839)
Other comprehensive income (loss)					(23)
Ending balance at Jun. 30, 2020	$ 17	813,468	(60)	(448,451)	364,974
Ending balances (in shares) at Jun. 30, 2020	170,709
Beginning balance at Mar. 31, 2020	$ 15	650,470	(60)	(439,885)	210,540
Beginning balances (in shares) at Mar. 31, 2020	151,584
Net income (loss)				(8,566)	(8,566)
Stock-based compensation expense		7,620			7,620
Issuance of common stock upon exercise of stock options		5,347			5,347
Issuance of common stock upon exercise of stock options (in shares)	1,464
Taxes paid related to net share settlement of equity awards		(1,740)			(1,740)
Taxes paid related to net share settlement of equity awards (in shares)	411
Issuance of common stock upon follow-on public offering, net of issuance costs	$ 2	151,771			151,773
Issuance of common stock upon follow-on public offering, net of issuance costs (in shares)	17,250
Ending balance at Jun. 30, 2020	$ 17	$ 813,468	$ (60)	$ (448,451)	$ 364,974
Ending balances (in shares) at Jun. 30, 2020	170,709