Investments - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Oct. 31, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Gain from sale of investment	$ 500,000		$ 0	$ 1,042,000	$ 0	$ 1,480,000
Class A Common Stock
Schedule of Equity Method Investments [Line Items]
Common stock value		$ 1,200,000
Real Goods Solar
Schedule of Equity Method Investments [Line Items]
Carrying value of investment	$ 0			$ 0		0
Real Goods Solar | Class A Common Stock
Schedule of Equity Method Investments [Line Items]
Gain from sale of investment						$ 1,000,000