Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value of Assets and Liabilities Measured on a Recurring Basis [Roll Forward]
Fair Value, Beginning Balance	$ 51,177	$ 44,681
Investment accretion	3,451	3,111
Unrealized losses included in interest expense	(48)	(48)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	1,678	1,673	1,667
Unrealized gains (losses) included in equity and partners’ capital	(2,454)	1,760
Fair Value, Ending Balance	53,804	51,177	44,681
Fair Value, Inputs, Level 2 [Member] | Available for sale [Member]
Fair Value of Assets and Liabilities Measured on a Recurring Basis [Roll Forward]
Fair Value, Beginning Balance	59,145	51,693
Investment accretion	3,451	3,111
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	(4,188)	4,341
Fair Value, Ending Balance	58,408	59,145
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Fair Value of Assets and Liabilities Measured on a Recurring Basis [Roll Forward]
Fair Value, Beginning Balance	(7,968)	(7,012)
Investment accretion
Unrealized losses included in interest expense	(48)	(48)
Losses on interest rate swaps reclassified into interest expense from accumulated other comprehensive loss	1,678	1,673
Unrealized gains (losses) included in equity and partners’ capital	1,734	(2,581)
Fair Value, Ending Balance	$ (4,604)	$ (7,968)