Borrowings - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended				6 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 25, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Hercules [Member]	Sep. 30, 2014 Silver Creek Convertible Note [Member]	Sep. 30, 2014 Silver Creek Convertible Note [Member] Silver Creek [Member]	Sep. 30, 2014 Silver Creek Convertible Note [Member] Minimum [Member] Silver Creek [Member]	Dec. 31, 2014 Scenario, Forecast [Member] Silver Creek Convertible Note [Member] Silver Creek [Member]	Sep. 30, 2014 Loan and Security Agreement [Member]	Sep. 30, 2013 Loan and Security Agreement [Member]	Sep. 30, 2014 Loan and Security Agreement [Member]	Sep. 30, 2013 Loan and Security Agreement [Member]	Nov. 30, 2012 Loan and Security Agreement [Member] Hercules [Member]	Jul. 31, 2013 4.50% Convertible Senior Notes [Member]	Jul. 31, 2013 4.50% Convertible Senior Notes [Member]	Sep. 30, 2014 4.50% Convertible Senior Notes [Member]	Sep. 30, 2013 4.50% Convertible Senior Notes [Member]	Sep. 30, 2014 4.50% Convertible Senior Notes [Member]	Sep. 30, 2013 4.50% Convertible Senior Notes [Member]
Schedule Of Debt Instruments [Line Items]
Gross proceeds from the debt issuance								$ 700,000									$ 125,000,000
Net proceeds from the debt issuance																	120,600,000
Interest rate (as a percent)										6.00%						4.50%	4.50%	4.50%		4.50%
Debt Maturity Date				Jul. 15, 2020
Conversion rate of common stock shares per $1,000 principal amount																160
Conversion ratio, principal amount																1,000	1,000
Initial conversion price of shares (in dollars per share)																$ 6.25	$ 6.25
Underwriting discounts and commissions and offering expenses																4,400,000
Interest expense		4,585,000	3,946,000	13,666,000	6,459,000						1,200,000	1,200,000	3,600,000	3,700,000				3,400,000	2,800,000	10,300,000	2,800,000
Aggregate principal amount of loans received															40,000,000
Extension period for interest-only payment	4 months
Amortization schedule of loan agreement				30 months
Beginning date for equal monthly installments of loan agreement				Feb. 01, 2015
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
Less unamortized discount						1,600,000												46,409,000		46,409,000
Amount of gross proceeds from qualifying equity financing in which holders would automatically convert into the next qualifying equity financing at a 25% discount									4,000,000
Discount on automatic conversion into the next qualifying equity financing (as a percent)								25.00%
Outstanding borrowings net							$ 600,000											$ 158,750,000		$ 158,750,000