Consolidated Statements of Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data	Convertible Preferred Stock [Member] USD ($)	Common Stock [Member] Initial Public Offering [Member] USD ($)	Common Stock [Member] Follow-On Offering [Member] USD ($)	Common Stock [Member] Investor Warrants [Member] USD ($)	Common Stock [Member] ORIX Warrants [Member]	Common Stock [Member] Lender Warrant [Member]	Common Stock [Member] USD ($)	Additional Paid-In Capital [Member] Initial Public Offering [Member] USD ($)	Additional Paid-In Capital [Member] Follow-On Offering [Member] USD ($)	Additional Paid-In Capital [Member] Investor Warrants [Member] USD ($)	Additional Paid-In Capital [Member] USD ($)	Accumulated Deficit [Member] USD ($)	Initial Public Offering [Member] USD ($)	Follow-On Offering [Member] USD ($)	Investor Warrants [Member] USD ($)	Total USD ($)
Beginning Balance at Dec. 31, 2011	$ 33,965						$ 2				$ 18,596	$ (74,620)				$ (22,057)
Beginning Balance (in shares) at Dec. 31, 2011	17,645,000						1,546,000
Issuance of common stock (in shares)		7,475,000	1,000,000	3,039,000	43,000
Issuance of common stock		7	1	3				57,023	15,546	1,737			57,030	15,547	1,740
Conversion of preferred stock to common stock (in shares)	(17,645,000)						17,688,000
Conversion of preferred stock to common stock	(33,965)						18				118,416					84,469
Conversion of preferred stock warrants to common stock warrants											738					738
Exercise of stock options (in shares)							701,000
Exercise of stock options							1				4,391					4,392
Issuance of common stock under Employee Stock Purchase Plan (in shares)							87,000
Issuance of common stock under Employee Stock Purchase Plan											852					852
Share repurchases (in shares)							(8,000)
Share repurchases											(113)					(113)
Tax benefit from the exercise of stock options											1,865					1,865
Stock-based compensation											3,750					3,750
Accretion of redemption premium											(2,301)					(2,301)
Net income												10,499				10,499
Ending Balance at Dec. 31, 2012							32				220,500	(64,121)				156,411
Ending Balance (in shares) at Dec. 31, 2012							31,571,000
Issuance of common stock (in shares)			500,000	351,000		117,000
Issuance of common stock			1						10,721					10,722
Exercise of stock options (in shares)							2,118,000
Exercise of stock options							2				15,979					15,981
Issuance of common stock under Employee Stock Purchase Plan (in shares)							89,000
Issuance of common stock under Employee Stock Purchase Plan											1,817					1,817
Tax benefit from the exercise of stock options											12,296					12,296
Stock-based compensation											9,206					9,206
Net income												21,699				21,699
Ending Balance at Dec. 31, 2013							35				270,519	(42,422)				228,132
Ending Balance (in shares) at Dec. 31, 2013							34,746,000
Exercise of stock options (in shares)							648,000									648,000
Exercise of stock options							1				6,743					6,744
Issuance of common stock under Employee Stock Purchase Plan (in shares)							60,000									59,535
Issuance of common stock under Employee Stock Purchase Plan											2,100					2,100
Restricted stock units (in shares)							25,000
Restricted stock units											(785)					(785)
Tax benefit from the exercise of stock options											10,433					10,433
Stock-based compensation											14,558					14,558
Net income												18,242				18,242
Ending Balance at Dec. 31, 2014							$ 36				$ 303,568	$ (24,180)				$ 279,424
Ending Balance (in shares) at Dec. 31, 2014							35,479,000