Derivatives and Hedging Activities Narratives (Details) - USD ($)		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 28, 2019
Derivative [Line Items]
Variation margin cash payment reported as a finacing activity in the statements of cash flows		$ 107,123,000	$ 4,002,000
Reclassifications from accumulated other comprehensive loss into earnings as a result of the discontinuance of cash-flow hedges		$ 0	$ 0	$ 0
Maximum length of time which we are hedging our exposure to the variability in future cash flows for forecasted transactions		1 year
Deferred net losses on derivatives accumulated in other comprehensive loss related to cash flow hedges expected to be reclassified to earnings during the next 12 months		$ 6,800,000
Aggregate fair value of all uncleared derivatives in a net-liability position (before cash collateral and related accrued interest)		88,300,000
Post-haircut value of collateral already posted		86,200,000
Rating Downgrade from AAPlus to AA or AAMinus [Member]
Derivative [Line Items]
Incremental collateral	[1]	579,000
Rating Downgrade From AAMinus to APlus, A or AMinus [Member]
Derivative [Line Items]
Incremental collateral	[1]	0
Rating Downgrade From AMinus to below AMinus [Member]
Derivative [Line Items]
Incremental collateral	[1]	7,513,000
Terminated Derivative [Member]
Derivative [Line Items]
Terminated derivatives notional amount					$ 611,900,000
Terminated derivatives settlement amount					(251,500,000)
Replacement Derivatives [Member]
Derivative [Line Items]
Replacement derivatives notional amount					611,900,000
Replacement derivatives settlement amount					$ 251,500,000
Cleared derivatives [Member]
Derivative [Line Items]
Delivered variation margin to clearing members		480,400,000
Variation margin cash payment reported as an operating activity in the statements of cash flows		373,300,000
Variation margin cash payment reported as a finacing activity in the statements of cash flows		$ 107,100,000

[1] Ratings are expressed in this table according to S&P's conventions but include the equivalent of such rating by Moody's. If there is a split rating, the lower rating is used.