Convertible and Long-term Debt Obligations - Full Repayment of DOE Loan Facility and Expiration of DOE Warrant - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2014 SecurityLoan	Mar. 31, 2013 DOE warrant [Member]	Sep. 30, 2014 DOE Loan Facility [Member]	Sep. 30, 2014 Series E convertible preferred stock [Member]
Debt Instrument [Line Items]
Loan facility, initiation date	Jan. 20, 2010
Number of multi-draw term loan facilities available	2
Multi-draw term loan facilities aggregate principal amount	$ 465.0
Warrant issued to DOE, shares purchasable	3,090,111			9,255,035
Exercise price of the warrant issued, price per share	$ 7.54			$ 2.51
Fair value of the DOE warrant		10.7
Debt instrument fair value		0
Debt instrument payment including principal and interest			451.8
Debt instrument payment of outstanding amount			441.0
Debt instrument penalty for early repayment			10.8
Reserve for loan repayment			$ 29.3