Held-to-Maturity Securities Redemption Terms (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		$ 947,142	$ 1,424,176
Carrying Value	[1],[2]	871,107	1,295,023
Fair Value		1,035,410	1,528,929
Other Than Mortgage-backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, Amortized Cost		3,090	1,043
Due in one year or less, Carrying Value	[1]	3,090	1,043
Due in one year or less, Fair Value		3,089	1,047
Due after one year through five years, Amortized Cost		0	6,205
Due after one year through five years, Carrying Value	[1]	0	6,205
Due after one year through five years, Fair Value		0	6,196
Due after five years through 10 years, Amortized Cost		15,405	16,865
Due after five years through 10 years, Carrying Value	[1]	15,405	16,865
Due after five years through 10 years, Fair Value		15,270	16,639
Due after 10 years, Amortized Cost		68,755	80,560
Due after 10 years, Carrying Value	[1]	68,755	80,560
Due after 10 years, Fair Value		65,046	76,183
Amortized Cost		87,250	104,673
Carrying Value	[1]	87,250	104,673
Fair Value		83,405	100,065
MBS [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	[3]	859,892	1,319,503
Carrying Value	[1],[3]	783,857	1,190,350
Fair Value	[3]	$ 952,005	$ 1,428,864

[1] Carrying value of held-to-maturity securities represents the sum of amortized cost and the amount of noncredit-related other-than-temporary impairment recognized in accumulated other comprehensive loss.

[2] Fair values of held-to-maturity securities were $1,035,410 and $1,528,929 at December 31, 2019 and 2018, respectively.

[3] MBS are not presented by contractual maturity because their expected maturities will likely differ from contractual maturities because borrowers of the underlying loans may have the right to call or prepay their obligations with or without call or prepayment fees.