Equity Method Investments - Activity Related to Equity Method Investments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Equity Method Investments
Balance at beginning of period	$ 103,517,000	$ 68,029,000
Contributions	11,652,000	5,078,000
Earnings (loss) on equity method investments	2,009,000	1,421,000
Balance at end of period	$ 117,178,000	74,528,000
Constitution
Schedule of Equity Method Investments [Line Items]
Ownership percentage	25.00%
Equity Method Investments
Balance at beginning of period	$ 90,345,000	64,268,000
Contributions	6,250,000	3,000,000
Earnings (loss) on equity method investments	2,011,000	1,427,000
Balance at end of period	$ 98,606,000	68,695,000
Meade
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%
Equity Method Investments
Balance at beginning of period	$ 13,172,000	3,761,000
Contributions	5,402,000	2,078,000
Earnings (loss) on equity method investments	(2,000)	(6,000)
Balance at end of period	18,572,000	$ 5,833,000
Minimum | Investment Commitment
Equity Method Investments
Commitment to fund equity method investments	30,000,000
Maximum | Investment Commitment
Equity Method Investments
Commitment to fund equity method investments	$ 35,000,000