Derivative Instruments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Interest_Rate_Swaps	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Interest_Rate_Swaps	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			$ 7,222
Amount of loss on derivative instruments recognized in income			$ (4)	$ (2)
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Interest_Rate_Swaps	1		1
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ (2,157)	$ 1,076	$ (6,945)	(5,181)
Derivative, lower fixed interest rate (percentage)	1.77%		1.77%
Estimated gain (loss) expected to be reclassified from accumulated other comprehensive income to income			$ (5,400)
Derivative liability, termination value	$ 11,000		$ 11,000
LIBOR [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative instrument, term for variable interest rate			1 month
Minimum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, variable interest rate	1.00%		1.00%
Change in Fair Value of Derivative Instruments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Amount of Gain (Loss) on Derivatives Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)		71
Interest Expense [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (1,057)	$ (3,213)	$ (7,222)	(9,720)
Gain (Loss) on Derivative Instruments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Amount of Gain (Loss) on Derivatives Recognized in Income (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0		(4)	$ (2)
Designated as Hedging Instrument [Member] | Other Accrued Liabilities [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Fair Value	0		0		$ 4,149
Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Fair Value	10,284		10,284		$ 6,105
Cash Flow Hedges [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Amount of Hedged Item	$ 1,000,000		$ 1,000,000
Cash Flow Hedges [Member] | Designated as Hedging Instrument [Member] | Fixed Interest Rate [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective fixed interest rate on hedged variable interest rate debt	5.02%		5.02%
July 2015 [Member] | Cash Flow Hedges [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 700,000		$ 700,000