Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance (in shares) at Dec. 31, 2017		37,765
Balance at Dec. 31, 2017	$ 23,291	$ 378	$ 232,960	$ (209,013)	$ (1,034)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,211			8,211
Forfeiture of dividend equivalent right	355			355
Other comprehensive income (loss)	0
Stock option exercises and employee stock plan purchases (in shares)		94
Stock option exercises and employee stock plan purchases	720	$ 1	719
Vesting of restricted stock awards and units (in shares)		174
Vesting of restricted stock awards and units	0	$ 2	(2)
Shares withheld to cover taxes (in shares)		(36)
Shares withheld to cover taxes	(709)	$ (1)	(708)
Stock-based compensation	1,796		1,796
Balance (in shares) at Mar. 31, 2018		37,997
Balance at Mar. 31, 2018	33,664	$ 380	234,765	(200,447)	(1,034)
Balance (in shares) at Dec. 31, 2017		37,765
Balance at Dec. 31, 2017	23,291	$ 378	232,960	(209,013)	(1,034)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,225
Other comprehensive income (loss)	2
Balance (in shares) at Sep. 30, 2018		38,463
Balance at Sep. 30, 2018	55,508	$ 385	237,588	(181,433)	(1,032)
Balance (in shares) at Mar. 31, 2018		37,997
Balance at Mar. 31, 2018	33,664	$ 380	234,765	(200,447)	(1,034)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,745			9,745
Other comprehensive income (loss)	4				4
Stock option exercises and employee stock plan purchases (in shares)		111
Stock option exercises and employee stock plan purchases	626	$ 1	625
Vesting of restricted stock awards and units (in shares)		286
Vesting of restricted stock awards and units	0	$ 3	(3)
Shares withheld to cover taxes (in shares)		(96)
Shares withheld to cover taxes	(1,722)	$ (1)	(1,721)
Stock-based compensation	2,216		2,216
Balance (in shares) at Jun. 30, 2018		38,298
Balance at Jun. 30, 2018	44,533	$ 383	235,882	(190,702)	(1,030)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,269			9,269
Other comprehensive income (loss)	(2)				(2)
Stock option exercises and employee stock plan purchases (in shares)		18
Stock option exercises and employee stock plan purchases	234		234
Vesting of restricted stock awards and units (in shares)		207
Vesting of restricted stock awards and units	0	$ 2	(2)
Shares withheld to cover taxes (in shares)		(60)
Shares withheld to cover taxes	(933)		(933)
Stock-based compensation	2,407		2,407
Balance (in shares) at Sep. 30, 2018		38,463
Balance at Sep. 30, 2018	55,508	$ 385	237,588	(181,433)	(1,032)
Balance (in shares) at Dec. 31, 2018		38,466
Balance at Dec. 31, 2018	71,002	$ 385	239,865	(168,140)	(1,108)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,949			9,949
Other comprehensive income (loss)	56				56
Stock option exercises and employee stock plan purchases (in shares)		37
Stock option exercises and employee stock plan purchases	606		606
Vesting of restricted stock awards and units (in shares)		365
Vesting of restricted stock awards and units	0	$ 4	(4)
Shares withheld to cover taxes (in shares)		(50)
Shares withheld to cover taxes	(1,120)	$ (1)	(1,119)
Stock-based compensation	2,720		2,720
Balance (in shares) at Mar. 31, 2019		38,818
Balance at Mar. 31, 2019	83,213	$ 388	242,068	(158,191)	(1,052)
Balance (in shares) at Dec. 31, 2018		38,466
Balance at Dec. 31, 2018	71,002	$ 385	239,865	(168,140)	(1,108)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,217
Other comprehensive income (loss)	111
Balance (in shares) at Sep. 30, 2019		39,229
Balance at Sep. 30, 2019	101,166	$ 392	248,694	(146,923)	(997)
Balance (in shares) at Mar. 31, 2019		38,818
Balance at Mar. 31, 2019	83,213	$ 388	242,068	(158,191)	(1,052)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,412			6,412
Other comprehensive income (loss)	88				88
Stock option exercises and employee stock plan purchases (in shares)		9
Stock option exercises and employee stock plan purchases	120		120
Vesting of restricted stock awards and units (in shares)		253
Vesting of restricted stock awards and units	0	$ 3	(3)
Shares withheld to cover taxes (in shares)		(37)
Shares withheld to cover taxes	(944)	$ (1)	(943)
Stock-based compensation	3,358		3,358
Balance (in shares) at Jun. 30, 2019		39,043
Balance at Jun. 30, 2019	92,247	$ 390	244,600	(151,779)	(964)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,856			4,856
Other comprehensive income (loss)	(33)				(33)
Stock option exercises and employee stock plan purchases (in shares)		49
Stock option exercises and employee stock plan purchases	1,020	$ 1	1,019
Vesting of restricted stock awards and units (in shares)		153
Vesting of restricted stock awards and units	0	$ 2	(2)
Shares withheld to cover taxes (in shares)		(16)
Shares withheld to cover taxes	(347)	$ (1)	(346)
Stock-based compensation	3,423		3,423
Balance (in shares) at Sep. 30, 2019		39,229
Balance at Sep. 30, 2019	$ 101,166	$ 392	$ 248,694	$ (146,923)	$ (997)