Strategic Partnerships - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Daimler Mercedes-Benz EV Program [Member]	Jun. 30, 2012 Daimler Mercedes-Benz EV Program [Member] Vehicle	Jun. 30, 2013 Daimler Mercedes-Benz EV Program [Member]	Oct. 31, 2010 Toyota RAV4 Program Phase 1 contract services agreement [Member]	Jun. 30, 2012 Toyota RAV4 Program Phase 1 contract services agreement [Member]	Oct. 31, 2010 Upfront payment arrangement [Member]	Jun. 30, 2013 Toyota supply and services agreement [Member]	Jun. 30, 2012 Toyota supply and services agreement [Member]	Jun. 30, 2013 Toyota supply and services agreement [Member]	Jun. 30, 2012 Toyota supply and services agreement [Member]
Limited Partners' Capital Account [Line Items]
Development services revenue recognized	$ 3,604,000	$ 4,599,000	$ 10,193,000	$ 15,521,000	$ 3,600,000	$ 4,300,000	$ 10,200,000		$ 10,700,000
Number of purchase orders						2
Future milestone payments							33,200,000	60,100,000
Revenue from automotive sales	401,535,000	22,054,000	956,738,000	41,299,000							13,300,000	4,400,000	27,700,000	4,700,000
Aggregate amount of payments received during period										$ 5,000,000