Subsequent Event - Additional Information (Detail) (Subsequent Event [Member])	1 Months Ended
	Oct. 31, 2013 Number
Subsequent Event [Line Items]
Long-term purchase of minimum lithium-ion battery cells	1,800,000,000
Purchase Agreement term	2014 through 2017
Original agreement date	Oct. 05, 2011
Supply Agreement [Member]
Subsequent Event [Line Items]
Extend term of Agreement	Two years until December 31, 2017