Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Common Stock	Common Stock IPO	Additional Paid-In Capital	Additional Paid-In Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2015			30,365,000
Beginning balance at Dec. 31, 2015	$ (185,289)		$ 303		$ 175,553		$ (359,160)	$ (1,985)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			41,000	6,200,000
Issuance of common stock	231	$ 48,820	$ 1	$ 62	230	$ 48,758
Net income	26,762						26,762
Other comprehensive income (loss)	$ 1,038							1,038
Stock option exercises (in shares)	40,976
Vesting of restricted stock awards (in shares)			214,000
Vesting of restricted stock awards	$ 0		$ 2		(2)
Shares withheld to cover taxes (in shares)			(64,000)
Vesting of restricted stock awards	(602)		$ (1)		(601)
Shares withheld to cover taxes	2,524				2,524
Ending balance (in shares) at Dec. 31, 2016			36,756,000
Ending balance at Dec. 31, 2016	(106,516)		$ 367		226,462		(332,398)	(947)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	123,385						123,385
Other comprehensive income (loss)	$ (87)							(87)
Stock option exercises (in shares)	465,232		478,000
Stock option exercises and employee stock plan purchases	$ 3,434		$ 5		3,429
Vesting of restricted stock awards (in shares)			744,000
Vesting of restricted stock awards	0		$ 8		(8)
Shares withheld to cover taxes (in shares)			(214,000)
Vesting of restricted stock awards	(2,853)		$ (2)		(2,851)
Shares withheld to cover taxes	5,928				5,928
Ending balance (in shares) at Dec. 31, 2017			37,765,000
Ending balance at Dec. 31, 2017	23,291		$ 378		232,960		(209,013)	(1,034)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,518						40,518
Forfeiture of dividend equivalent right	355						355
Other comprehensive income (loss)	(74)							(74)
Stock option exercises and employee stock plan purchases (in shares)			223,000
Stock option exercises and employee stock plan purchases	$ 1,580		$ 2		1,578
Stock option exercises (in shares)	192,550
Vesting of restricted stock awards (in shares)			672,000
Vesting of restricted stock awards	$ 0		$ 7		(7)
Shares withheld to cover taxes (in shares)			(194,000)
Vesting of restricted stock awards	(3,386)		$ (2)		(3,384)
Shares withheld to cover taxes	8,718				8,718
Ending balance (in shares) at Dec. 31, 2018			38,466,000
Ending balance at Dec. 31, 2018	$ 71,002		$ 385		$ 239,865		$ (168,140)	$ (1,108)