Fair Value Measurements (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Fair Value Assets and Liabilities Measured on Recurring Basis Fair value and input reconciliation [Roll Forward]
Fair Value, Beginning Balance	$ 55,770	$ 53,804
Investment accretion included in interest income	3,142	2,833
Unrealized losses included in interest expense	(36)	(36)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	1,260	1,265
Unrealized losses included in equity and partners’ capital	(1,568)	(2,106)
Fair Value, Ending Balance	58,568	55,760
Available-for-sale Securities [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Fair value and input reconciliation [Roll Forward]
Fair Value, Beginning Balance	61,043	58,408
Investment accretion included in interest income	3,142	2,833
Unrealized losses included in equity and partners’ capital	(51)	(618)
Fair Value, Ending Balance	64,134	60,623
Interest Rate Swap [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Fair value and input reconciliation [Roll Forward]
Fair Value, Beginning Balance	(5,273)	(4,604)
Unrealized losses included in interest expense	(36)	(36)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	1,260	1,265
Unrealized losses included in equity and partners’ capital	(1,517)	(1,488)
Fair Value, Ending Balance	$ (5,566)	$ (4,863)