CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in-Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Treasury Stock	Total
Balance at Dec. 31, 2017	$ 35	$ 331,073	$ (591)	$ (192,183)	$ (132)	$ 138,202
Balance (in shares) at Dec. 31, 2017	34,647				(28)
Stockholders' Deficit
Common stock issued under stock plans		2,839				2,839
Common stock issued under stock plans (in shares)	208
Stock-based compensation		5,402				5,402
Other comprehensive income			(704)			(704)
Net loss				(2,711)		(2,711)
Balance at Mar. 31, 2018	$ 35	339,314	(1,295)	(194,894)	$ (132)	143,028
Balance (in shares) at Mar. 31, 2018	34,855				(28)
Balance at Dec. 31, 2017	$ 35	331,073	(591)	(192,183)	$ (132)	138,202
Balance (in shares) at Dec. 31, 2017	34,647				(28)
Stockholders' Deficit
Other comprehensive income						1,298
Net loss						(14,730)
Balance at Sep. 30, 2018	$ 36	369,709	707	(206,913)	$ (132)	163,407
Balance (in shares) at Sep. 30, 2018	35,995				(28)
Balance at Mar. 31, 2018	$ 35	339,314	(1,295)	(194,894)	$ (132)	143,028
Balance (in shares) at Mar. 31, 2018	34,855				(28)
Stockholders' Deficit
Common stock issued under stock plans		2,836				2,836
Common stock issued under stock plans (in shares)	311
Stock-based compensation		6,461				6,461
Other comprehensive income			1,606			1,606
Net loss				(5,398)		(5,398)
Balance at Jun. 30, 2018	$ 35	348,611	311	(200,292)	$ (132)	148,533
Balance (in shares) at Jun. 30, 2018	35,166				(28)
Stockholders' Deficit
Common stock issued under stock plans	$ 1	13,925				13,926
Common stock issued under stock plans (in shares)	829
Stock-based compensation		7,173				7,173
Other comprehensive income			396			396
Net loss				(6,621)		(6,621)
Balance at Sep. 30, 2018	$ 36	369,709	707	(206,913)	$ (132)	163,407
Balance (in shares) at Sep. 30, 2018	35,995				(28)
Balance at Dec. 31, 2018	$ 36	378,352	738	(205,134)	$ (132)	$ 173,860
Balance (in shares) at Dec. 31, 2018	36,135				(28)	36,107
Stockholders' Deficit
Common stock issued under stock plans		5,406				$ 5,406
Common stock issued under stock plans (in shares)	226
Stock-based compensation		7,129				7,129
Other comprehensive income			436			436
Net loss				(1,342)		(1,342)
Balance at Mar. 31, 2019	$ 36	390,887	1,174	(206,476)	$ (132)	185,489
Balance (in shares) at Mar. 31, 2019	36,361				(28)
Balance at Dec. 31, 2018	$ 36	378,352	738	(205,134)	$ (132)	$ 173,860
Balance (in shares) at Dec. 31, 2018	36,135				(28)	36,107
Stockholders' Deficit
Other comprehensive income						$ 1,099
Net loss						(21,157)
Balance at Sep. 30, 2019	$ 37	414,665	1,837	(226,291)	$ (132)	$ 190,116
Balance (in shares) at Sep. 30, 2019	36,945				(28)	36,917
Balance at Mar. 31, 2019	$ 36	390,887	1,174	(206,476)	$ (132)	$ 185,489
Balance (in shares) at Mar. 31, 2019	36,361				(28)
Stockholders' Deficit
Common stock issued under stock plans	$ 1	318				319
Common stock issued under stock plans (in shares)	305
Stock-based compensation		8,247				8,247
Other comprehensive income			59			59
Net loss				(6,309)		(6,309)
Balance at Jun. 30, 2019	$ 37	399,452	1,233	(212,785)	$ (132)	187,805
Balance (in shares) at Jun. 30, 2019	36,666				(28)
Stockholders' Deficit
Common stock issued under stock plans		6,666				6,666
Common stock issued under stock plans (in shares)	279
Stock-based compensation		8,547				8,547
Other comprehensive income			604			604
Net loss				(13,506)		(13,506)
Balance at Sep. 30, 2019	$ 37	$ 414,665	$ 1,837	$ (226,291)	$ (132)	$ 190,116
Balance (in shares) at Sep. 30, 2019	36,945				(28)	36,917