Derivatives and Hedging Activities Derivatives in Statement of Income and Impact on Other Income/Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains related to derivatives not designated as hedging instruments		$ 1,419
Net gains on derivatives and hedging activities			$ 2,336	$ 551
Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains (losses) related to fair-value hedges	[1]		2,027	(2,308)
Total net gains related to cash-flow hedges	[2]		227	280
Total net gains (losses) related to derivatives designated as hedging instruments			2,254	(2,028)
Total net gains related to derivatives not designated as hedging instruments		1,331	1,103	2,202
Other	[3]		(1,021)	377
Net gains on derivatives and hedging activities			2,336	551
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other	[3]	88
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gains on derivatives and hedging activities		1,419
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 gains related to derivatives not designated as hedging instruments		(614)	682	434
Mortgage Receivable [Member] | Mortgage-delivery commitments [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gains related to derivatives not designated as hedging instruments		$ 1,945	$ 421	$ 1,768

[1] Consists of interest-rate swaps.

[2] Consists of forward-start interest-rate swaps.

[3] Consists of price alignment amount on derivatives for which variation margin is characterized as a daily settlement amount.