Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Common Stock	Common Stock IPO	Treasury Stock	Additional Paid-In Capital	Additional Paid-In Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2014			18,081,000		(5,000)
Beginning balance at Dec. 31, 2014	$ (239,270)		$ 181		$ (106)	$ 106,699		$ (344,414)	$ (1,630)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			40,000	12,257,000
Issuance of common stock	0	$ 67,177	$ 0	$ 122			$ 67,055
Treasury stock retired (in shares)					5,000
Treasury stock retired	0				$ 106	(106)
Net income (loss)	(14,746)							(14,746)
Other comprehensive income (loss)	$ (355)								(355)
Stock option exercises (in shares)	0
Shares withheld to cover taxes (in shares)			(13,000)
Shares withheld to cover taxes	$ (97)		$ 0			(97)
Stock-based compensation	2,002					2,002
Ending balance (in shares) at Dec. 31, 2015			30,365,000		0
Ending balance at Dec. 31, 2015	(185,289)		$ 303		$ 0	175,553		(359,160)	(1,985)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			6,200,000
Issuance of common stock	48,820		$ 62			48,758
Net income (loss)	26,762							26,762
Other comprehensive income (loss)	$ 1,038								1,038
Stock option exercises (in shares)	40,976
Stock option exercises	$ 231		$ 1			230
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)
Shares withheld to cover taxes	(602)		$ (1)			(601)
Stock-based compensation	2,524					2,524
Ending balance (in shares) at Dec. 31, 2016			36,756,000		0
Ending balance at Dec. 31, 2016	(106,516)		$ 367		$ 0	226,462		(332,398)	(947)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	123,385							123,385
Other comprehensive income (loss)	$ (87)								(87)
Stock option exercises and employee stock plan purchases (in shares)	478,000
Stock option exercises and employee stock plan purchases	$ 3,434		$ 5			3,429
Stock option exercises (in shares)	465,232
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)
Shares withheld to cover taxes	(2,853)		$ (2)			(2,851)
Stock-based compensation	5,928					5,928
Ending balance (in shares) at Dec. 31, 2017			37,765,000		0
Ending balance at Dec. 31, 2017	$ 23,291		$ 378		$ 0	$ 232,960		$ (209,013)	$ (1,034)