CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Total	Common Stock and Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2017		35,950,518			6,686,690
Beginning balance at Dec. 31, 2017	$ 9,657	$ 228,046	$ 99	$ (171,616)	$ (46,872)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	57,485			57,485
Unrealized gain (loss) on available-for-sale securities, net of taxes	8		8
Issuance of common stock for employee stock purchase (in shares)		26,689
Issuance of common stock for employee stock purchase	218	$ 218
Exercise of stock options, net of shares withheld for employee taxes (in shares)		1,326,718			39,695
Exercise of stock options, net of shares withheld for employee taxes	8,011	$ 8,580			$ (569)
Release of restricted stock units and awards (in shares)		222,985
Release of restricted stock units and awards	0
Stock based compensation	6,266	$ 6,266
Ending balance (in shares) at Sep. 30, 2018		37,526,910			6,726,385
Ending balance at Sep. 30, 2018	100,397	$ 243,110	107	(95,379)	$ (47,441)
Beginning balance (in shares) at Jun. 30, 2018		37,488,535			6,726,385
Beginning balance at Jun. 30, 2018	101,957	$ 240,445	109	(91,156)	$ (47,441)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(4,640)			(4,640)
Unrealized gain (loss) on available-for-sale securities, net of taxes	(2)		(2)
Issuance of common stock for employee stock purchase (in shares)		12,855
Issuance of common stock for employee stock purchase	120	$ 120
Exercise of stock options, net of shares withheld for employee taxes (in shares)		4,687
Exercise of stock options, net of shares withheld for employee taxes	31	$ 31
Release of restricted stock units and awards (in shares)		20,833
Release of restricted stock units and awards	0
Stock based compensation	2,514	$ 2,514
Ending balance (in shares) at Sep. 30, 2018		37,526,910			6,726,385
Ending balance at Sep. 30, 2018	100,397	$ 243,110	107	(95,379)	$ (47,441)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of change in accounting policy				417
Beginning balance (in shares) at Dec. 31, 2018		37,652,498			6,823,147
Beginning balance at Dec. 31, 2018	99,660	$ 246,415	116	(98,521)	$ (48,350)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(21,023)			(21,023)
Unrealized gain (loss) on available-for-sale securities, net of taxes	16		16
Issuance of common stock for employee stock purchase (in shares)		21,741
Issuance of common stock for employee stock purchase	165	$ 165
Exercise of stock options, net of shares withheld for employee taxes (in shares)		173,131
Exercise of stock options, net of shares withheld for employee taxes	1,240	$ 1,240
Release of restricted stock units and awards (in shares)		771,552
Release of restricted stock units and awards	0
Stock based compensation	4,371	$ 4,371
Ending balance (in shares) at Sep. 30, 2019		38,618,922			6,823,147
Ending balance at Sep. 30, 2019	84,429	$ 252,191	132	(119,544)	$ (48,350)
Beginning balance (in shares) at Jun. 30, 2019		38,488,327			6,823,147
Beginning balance at Jun. 30, 2019	83,710	$ 250,079	138	(118,157)	$ (48,350)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,387)
Unrealized gain (loss) on available-for-sale securities, net of taxes	(6)		(6)
Issuance of common stock for employee stock purchase (in shares)		8,262
Issuance of common stock for employee stock purchase	56	$ 56
Exercise of stock options, net of shares withheld for employee taxes (in shares)		111,333
Exercise of stock options, net of shares withheld for employee taxes	869	$ 869
Release of restricted stock units and awards (in shares)		11,000
Release of restricted stock units and awards	0
Stock based compensation	1,187	$ 1,187
Ending balance (in shares) at Sep. 30, 2019		38,618,922			6,823,147
Ending balance at Sep. 30, 2019	$ 84,429	$ 252,191	$ 132	$ (119,544)	$ (48,350)