Members' Equity - AOCI (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	$ (7,099)
Deferred losses on interest rate swaps	(3,746)	(2,067)
Reclassification of unrealized loss on interest rate swaps into income	3,097	3,273
Unrealized loss on available-for-sale securities	(52)	3
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	3,097
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(52)
Accumulated other comprehensive loss, ending balance	(7,800)
Unrealized Gain (Loss) on Derivaitve Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(6,976)
Deferred losses on interest rate swaps	(3,746)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	3,097
Accumulated other comprehensive loss, ending balance	(7,625)
Unrealized Gain (Loss) on Available-For-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(123)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(52)
Accumulated other comprehensive loss, ending balance	$ (175)