Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	$ 53,804	$ 51,177
Investment accretion included in interest income	920	830
Unrealized losses included in interest expense	(12)	(12)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	426	420
Unrealized gains (losses) included in equity and partners’ capital	(294)	(1,532)
Fair Value, Ending Balance	54,844	50,883
Fair Value, Inputs, Level 2 [Member] | Available for sale [Member]
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	58,408	59,145
Investment accretion included in interest income	920	830
Unrealized losses included in interest expense
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss
Unrealized gains (losses) included in equity and partners’ capital	467	(1,708)
Fair Value, Ending Balance	59,795	58,267
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	(4,604)	(7,968)
Investment accretion included in interest income
Unrealized losses included in interest expense	(12)	(12)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	426	420
Unrealized gains (losses) included in equity and partners’ capital	(761)	176
Fair Value, Ending Balance	$ (4,951)	$ (7,384)