Investment in Unconsolidated Affiliates - Summary of Financial Information (Details) - Solar Gen Two Project Entity and North Star, Significant Investees - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	May 31, 2016	Jun. 30, 2015	May 31, 2016	Jun. 30, 2015
Summary statements of operations information:
Revenue	$ 16,101	$ 13,317	$ 24,751	$ 21,061
Operating expenses	9,844	8,509	20,769	16,359
Net income	$ 6,382	$ 4,932	$ 4,212	$ 4,832