Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	$ 44,681	$ (2,746)
Investment accretion	748
Unrealized gains (losses) included in earnings	(12)	(12)
Realized gains (losses) included in earnings
Unrealized gains (losses) included in equity and partners' capital	2,864	(57)
Fair Value, Ending Balance	48,281	(2,701)
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	51,693
Investment accretion	748
Realized gains (losses) included in earnings
Unrealized gains (losses) included in equity and partners' capital	2,573
Fair Value, Ending Balance	55,014
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	(7,012)	(2,746)
Unrealized gains (losses) included in earnings	(12)	(12)
Realized gains (losses) included in earnings
Unrealized gains (losses) included in equity and partners' capital	291	(57)
Fair Value, Ending Balance	(6,733)	(2,701)
Fair Value Inputs Level 3 [Member] | Total rate of return swaps [Member]
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	(5,841)	(19,542)
Unrealized gains (losses) included in earnings	(936)	3,478
Realized gains (losses) included in earnings
Fair Value, Ending Balance	(4,905)	(16,064)
Fair Value Inputs Level 3 [Member] | Total rate of return debt [Member]
Fair value of assets and liabilities measured on a recurring basis
Fair Value, Beginning Balance	5,841	19,542
Unrealized gains (losses) included in earnings	(936)	(3,478)
Realized gains (losses) included in earnings
Fair Value, Ending Balance	$ 4,905	$ 16,064