Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data	Total	Series A -1 Convertible Preferred Stock [Member]	Series A -2 Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]	Series A -1 Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2011	$ (55,707)	$ 9,217	$ 15,837	$ 41,495	$ 15,854			$ 2	$ 7,732	$ 1	$ (63,442)
Beginning balance, shares at Dec. 31, 2011		12,981,000	22,304,000	115,204,000	39,943,000			205,000
Issuance of stock, net of issuance costs						59,831
Issuance of stock, shares						120,409,000
Accretion and dividends on convertible preferred stock	(3,057)	194	332	1,689	673	169			(3,057)
Gain on extinguishment of convertible preferred stock	23,114	(7,074)	(9,032)	(2,863)	(4,145)
Reclassification of Series A-1 Preferred Stock	2,337	(2,337)					2,337
Reclassification of Series A-1 Preferred Stock, shares		(12,981,000)					12,981,000
Reclassification of Series A-1 Preferred Stock warrants	394								394
Vesting of restricted stock issued in exchange for nonrecourse note								1	(1)
Vesting of restricted stock issued in exchange for nonrecourse note (in shares)								82,000
Vesting of restricted stock								12,000
Exercise of stock options	21								21
Exercise of stock options, shares								10,000
Realized gain on marketable securities	(1)									(1)
Stock-based compensation	822								822
Net loss	(23,670)										(23,670)
Gain on extinguishment of convertible preferred stock	23,114								9,356		13,758
Ending balance at Dec. 31, 2012	(55,747)		7,137	40,321	12,382	60,000	2,337	3	15,267		(73,354)
Ending balance, shares at Dec. 31, 2012			22,304,000	115,204,000	39,943,000	120,409,000	12,981,000	309,000
Reclassification of Series A-1 Preferred Stock warrants	655								655
Vesting of restricted stock issued in exchange for nonrecourse note (in shares)								41,000
Vesting of restricted stock								45,000
Proceeds from IPO, net of closing costs of $11,229	104,921							69	104,852
Proceeds from IPO, net of closing shares								6,832,000
Conversion of convertible preferred stock into common stock	119,841		(7,137)	(40,321)	(12,382)	(60,000)	(2,337)	164	122,014
Conversion of convertible preferred stock into common stock, shares			(22,304,000)	(115,204,000)	(39,943,000)	(120,409,000)	(12,981,000)	16,389,000
Repayment of nonrecourse note	344								344
Exercise of common stock warrants								1	(1)
Exercise of common stock warrants, shares								102,000
Exercise of stock options	483							2	481
Exercise of stock options, shares								222,000
Stock-based compensation	6,491								6,491
Net loss	(25,321)										(25,321)
Ending balance at Dec. 31, 2013	151,667							239	250,103		(98,675)
Ending balance, shares at Dec. 31, 2013								23,940,000
Issuance of stock, net of issuance costs	353,042							65	352,977
Issuance of stock, shares								6,498,000
Vesting of restricted stock issued in exchange for nonrecourse note								1	(1)
Vesting of restricted stock issued in exchange for nonrecourse note (in shares)								69,000
Issuance of common stock in connection with acquisition	19,474							4	19,470
Issuance of common stock in connection with acquisition, shares								411,000
Exercise of common stock warrants								1	(1)
Exercise of common stock warrants, shares								114,000
Exercise of stock options	5,049							13	5,036
Exercise of stock options, shares	1,313,031							1,306,000
Issuance of common stock in exchange for consulting services to non-employees	42								42
Issuance of common stock in exchange for consulting services, shares								2,000
Stock-based compensation	10,763								10,763
Unrealized loss on available-for-sale securities, net of tax	(71)									(71)
Net loss	(48,709)										(48,709)
Ending balance at Dec. 31, 2014	$ 491,257							$ 323	$ 638,389	$ (71)	$ (147,384)
Ending balance, shares at Dec. 31, 2014								32,340,000