Derivative Instruments (Details) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended										3 Months Ended	9 Months Ended		3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Interest Rate Swap [Member] Interest_Rate_Swaps	Sep. 30, 2012 Interest Rate Swap [Member]	Sep. 30, 2013 Interest Rate Swap [Member] Interest_Rate_Swaps	Sep. 30, 2012 Interest Rate Swap [Member]	Sep. 30, 2013 Cash Flow Hedges [Member] Interest_Rate_Swaps	Sep. 30, 2012 Cash Flow Hedges [Member]	Sep. 30, 2013 Cash Flow Hedges [Member] Interest_Rate_Swaps	Sep. 30, 2013 LIBOR [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Minimum [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Amended Interest Rate Swap [Member] Interest Rate Swap [Member] Interest_Rate_Swaps	Sep. 30, 2013 Interest Expense, Net [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Interest Expense, Net [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Interest Expense, Net [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Interest Expense, Net [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Change in Fair Value of Derivative Instruments [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Change in Fair Value of Derivative Instruments [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Change in Fair Value of Derivative Instruments [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Change in Fair Value of Derivative Instruments [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Products [Member]	Sep. 30, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Products [Member]		Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Products [Member]	Sep. 30, 2012 Not Designated as Hedging Instrument [Member] Interest Rate Products [Member]		Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Other Long-term Liabilities [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Other Long-term Liabilities [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Other Long-term Liabilities [Member] Interest Rate Swap [Member]	Dec. 31, 2012 Designated as Hedging Instrument [Member] Other Long-term Liabilities [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Cash Flow Hedges [Member] Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Cash Flow Hedges [Member] Designated as Hedging Instrument [Member] Fixed Interest Rate [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Opco [Member] Minimum [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Propco [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Sep. 30, 2013 Propco [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Sep. 30, 2012 Propco [Member] Not Designated as Hedging Instrument [Member] Interest Rate Swap [Member]	Sep. 30, 2012 GVR [Member] Cash Flow Hedges [Member]
Derivative [Line Items]
Number of derivative instruments held			2		2		2		2			1
Derivative, lower fixed interest rate (percentage)			1.77%		1.77%
Derivative, higher fixed interest rate (percentage)			2.13%		2.13%
Derivative instrument, term for variable interest rate										1 month
Derivative, description of variable rate basis					LIBOR
Derivative, fixed interest rate											1.00%																						1.00%
Fixed interest rate on debt instruments resulting from interest rate swap																																6.00%
Derivative instruments, deferred losses recognized in other comprehensive income									$ 1,100,000
Notional amount of interest rate derivatives			1,100,000,000		1,100,000,000
Long-term debt, percentage bearing fixed interest, amount																															1,100,000,000
Derivative liability, fair value																											0	2,746,000	15,512,000	21,140,000
Amount of Loss on Derivatives Recognized in Other Comprehensive Income (Effective Portion)			(4,468,000)	(5,705,000)	1,125,000	(18,626,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Income into Income (Effective Portion)													(3,346,000)	(3,189,000)	(9,821,000)	(9,484,000)
Amount of Loss on Derivatives Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)							43,000	779,000	77,000								(43,000)	(779,000)	(77,000)	(779,000)																	741,000
Estimated gain (loss) expected to be reclassified from accumulated other comprehensive income to income					12,800,000
Period for deferred losses on cash flow hedges to be reclassified to earnings									12 months
Amount of Loss on Derivative Instruments Recognized in Income	(281,000)	(800,000)																			0	(21,000)	[1]	(204,000)	(21,000)	[1]								21,000	200,000	21,000
Derivative liability, termination value			$ 17,200,000		$ 17,200,000

[1] During the three months ended September 30, 2013, all of the Company's interest rate swaps were designated in hedging relationships.