Consolidated Statements of Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Common Stock 2009 Convertible Notes and accrued interest	Common Stock 2009 Secured Notes and accrued interest	Additional Paid-In Capital	Additional Paid-In Capital 2009 Secured Notes and accrued interest	Additional Paid-In Capital HBM Secured Notes and accrued interest and early prepayment penalty	Accumulated Deficit	Treasury Stock	Accumulated Other Comprehensive Income
Balances at Dec. 31, 2011	$ 48,269	$ 25			$ 228,470			$ (180,239)	$ (2)	$ 15
Balances (in shares) at Dec. 31, 2011		25,339,000
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	770	1			769
Exercise of stock options (in shares)		279,000
Net loss	100				100
Exercise of warrants (in shares)		105,000
Exercise of warrants	4,776				4,776
Stock-based compensation		0
Initial public offering, net of issuance costs (in shares)		0
Exercise of stock options	62,855	7			62,848
Follow-on public offering, net of issuance costs (in shares)		6,900,000
Conversion of Convertible Notes and accrued interest			0
Conversion of Convertible Notes (in shares)			0
Conversion of Secured Notes and accrued interest and early prepayment penalty				0		0
Conversion of Secured Notes and accrued interest and early prepayment penalty (in shares)				0
Unrealized gain (loss) on short-term investments	12									12
Shares issued under employee stock purchase plan	1,354				1,354
Net loss	(52,281)							(52,281)
Balances at Dec. 31, 2012	65,855	33			298,317			(232,520)	(2)	27
Balances (in shares) at Dec. 31, 2012		32,623,000
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	3,856	1			3,855
Exercise of stock options (in shares)		741,000
Net loss	0				0
Exercise of warrants (in shares)		271,000
Exercise of warrants	11,513				11,513
Exercise of stock options	110,452
Conversion of Secured Notes and accrued interest and early prepayment penalty							0
Unrealized gain (loss) on short-term investments	(22)									(22)
Equity component of convertible senior notes, net of issuance costs	23,956				23,956
Issuance of common stock from treasury					(2)				2
Issuance of common stock from treasury (in shares)		1,000
Net loss	(63,909)							(63,909)
Balances at Dec. 31, 2013	41,249	34			337,639			(296,429)	0	5
Balances (in shares) at Dec. 31, 2013		33,636,000
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	7,239	0			7,239
Exercise of stock options (in shares)		624,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	15,722	16,000
Stock Issued During Period, Value, Employee Stock Purchase Plan		0			1,184
Net loss	0
Exercise of warrants (in shares)		35,000
Exercise of warrants	24,822				24,822
Exercise of stock options		2			110,450
Follow-on public offering, net of issuance costs (in shares)		1,840,000
Conversion of Secured Notes and accrued interest and early prepayment penalty							0
Unrealized gain (loss) on short-term investments	(85)									(85)
Shares issued under employee stock purchase plan	1,184
Net loss	(13,716)							(13,716)
Balances at Dec. 31, 2014	$ 171,145	$ 36			$ 481,334			$ (310,145)	$ 0	$ (80)
Balances (in shares) at Dec. 31, 2014		36,151,000