Derivative Instruments (Gross Fair Value of Derivative Instruments) (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Derivatives Fair Value [Line Items]
Asset Derivatives, Fair Value		$ 38,428	$ 18,529
Liability Derivatives, Fair Value		31,213	46,110
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest rate contracts [Member] | Other Noncurrent Assets [Member]
Derivatives Fair Value [Line Items]
Asset Derivatives, Fair Value		36,743	18,466
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest rate contracts [Member] | Other Assets Current [Member]
Derivatives Fair Value [Line Items]
Asset Derivatives, Fair Value	[1]	1,685	63
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest rate contracts [Member] | Other Long-term Obligations [Member]
Derivatives Fair Value [Line Items]
Liability Derivatives, Fair Value		30,743	45,100
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest rate contracts [Member] | Accounts Payable and Accrued Liabilities [Member]
Derivatives Fair Value [Line Items]
Liability Derivatives, Fair Value	[1]	$ 470	$ 1,010

[1] Derivative instruments that mature within one year, as a whole, are classified as current.