Fair Value Measurements (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 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	2,068	1,864
Unrealized losses included in interest expense	(24)	(24)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	842	844
Unrealized losses included in equity and partners’ capital	(1,787)	(1,478)
Fair Value, Ending Balance	56,869	55,010
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	2,068	1,864
Unrealized losses included in equity and partners’ capital	(1,162)	(51)
Fair Value, Ending Balance	61,949	60,221
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	(24)	(24)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	842	844
Unrealized losses included in equity and partners’ capital	(625)	(1,427)
Fair Value, Ending Balance	$ (5,080)	$ (5,211)