Borrowings (Details) (USD $)	1 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended				1 Months Ended		3 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended
	Jul. 31, 2013	Sep. 30, 2013	Jul. 31, 2013 Minimum	Sep. 30, 2013 Loan and Security Agreement	Sep. 30, 2013 Loan and Security Agreement	Jul. 31, 2013 Loan and Security Agreement Minimum	Oct. 27, 2013 Loan and Security Agreement Hercules	Sep. 30, 2013 Loan and Security Agreement Hercules	Nov. 30, 2012 Loan and Security Agreement Hercules	Feb. 28, 2013 Convertible notes Silver Creek	Dec. 31, 2012 Convertible notes Silver Creek	Sep. 30, 2013 Convertible notes Silver Creek	Sep. 30, 2013 Convertible notes Silver Creek	Jul. 31, 2013 4.50% Convertible Senior Notes	Sep. 30, 2013 4.50% Convertible Senior Notes	Sep. 30, 2013 4.50% Convertible Senior Notes	Jul. 31, 2013 4.50% Convertible Senior Notes Conversion Terms, Fundamental Changes	Jul. 31, 2013 4.50% Convertible Senior Notes Conversion Terms, Event of Default	Jul. 31, 2013 4.50% Convertible Senior Notes Minimum D	Jul. 31, 2013 4.50% Convertible Senior Notes Maximum
Debt
Aggregate principal amounts										$ 300,000	$ 1,600,000			$ 125,000,000		$ 125,000,000
Proceeds from issuance of convertible senior notes, net		120,621,000												120,600,000
Interest rate (as a percent)														4.50%	4.50%	4.50%
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible																			20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible														30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price that must be exceeded														130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period														5 days
Number of consecutive trading days before five consecutive business days during the note measurement period														5 days
Conversion ratio, principal amount														1,000
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation																				98.00%
Conversion rate of common stock shares per $1,000 principal amount														160.0000
Initial conversion price of shares (in dollars per share)														$ 6.25
Premium over public offering price (as a percent)														25.00%
Public offering price (in dollars per share)	$ 5.00
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest																	100.00%
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable																		25.00%
Percentage of principal amount due and payable upon event of default																		100.00%
Percentage of principal amount due and payable upon event of default arising out of certain bankruptcy events.																		100.00%
Effective interest rate used to compute initial fair value (as a percent)														15.00%
Fair value of indebtedness														71,200,000
Embedded conversion option														53,800,000
Underwriting discounts and commissions and offering expenses														4,400,000
Debt issuance costs allocated to unamortized debt discount														2,500,000
Debt issuance costs attributable to embedded conversion option														1,900,000
Interest expense				1,200,000	3,700,000							100,000	300,000		2,800,000	2,800,000
Outstanding borrowings, net								39,000,000				1,800,000	1,800,000		70,600,000	70,600,000
Debt discounts								1,100,000				100,000	100,000		54,400,000	54,400,000
Aggregate principal amount of loans received									40,000,000						125,000,000	125,000,000
Amount of gross proceeds in one or more transactions prior to December 1, 2013 that the Company may elect to extend the interest-only period by six months						75,000,000
Shares of common stock sold to public	5,750,000
Net proceeds from underwritten public offering and issuance of debt			75,000,000
Discount on loan recorded as a non-current liability to be paid upon full repayment or maturity of the loans				1,200,000	1,200,000
Future minimum payments under the loans payable, excluding interest
2014							8,372,000
2015							15,643,000
2016							15,985,000
Total							$ 40,000,000
Extension period for interest only payments					6 months
Period of interest-only payment					12 months