Derivatives in Statement of Income and Impact on Other Income/Loss (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Total net (losses) gains related to derivatives not designated as hedging instruments		$ (52,558)	$ 548
Net (losses) gains on derivatives not designated as hedging instruments		(52,558)	548
Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net (losses) gains related to derivatives not designated as hedging instruments			548
Price alignment interest	[1]		0
Net (losses) gains on derivatives not designated as hedging instruments			548
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Price alignment interest	[1]	73
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net (losses) gains related to derivatives not designated as hedging instruments		(52,558)
Net (losses) gains on derivatives not designated as hedging instruments		(52,558)
Interest-rate swaps [Member] | Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net (losses) gains related to derivatives not designated as hedging instruments		(52,569)	(60)
Net (losses) gains on derivatives not designated as hedging instruments		(52,569)	(60)
Mortgage Receivable [Member] | Mortgage-delivery commitments [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net (losses) gains related to derivatives not designated as hedging instruments		(62)	608
Net (losses) gains on derivatives not designated as hedging instruments		$ (62)	$ 608

[1] Relates to derivatives for which variation margin payments are characterized as daily settled contracts.