Investments Held-to-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	[1]	$ 733,647	$ 947,142
Carrying Value	[2],[3]	676,888	871,107
Fair Value		733,970	1,035,410
Other Than MBS [Member]
Debt Securities, Held-to-maturity, Maturity [Abstract]
Due in one year or less - Amortized Cos		3,090	3,090
Due in one year or less - Carrying Value	[2]	3,090	3,090
Due in one year or less - Fair Value		3,083	3,089
Due after one year through five years - Amortized Cost		0	0
Due after one year through five years - Carrying Value	[2]	0	0
Due after one year through five years - Fair Value		0	0
Due after five years through 10 years - Amortized Cost		15,405	15,405
Due after five years through 10 years - Carrying Value	[2]	15,405	15,405
Due after five years through 10 years - Fair Value		14,903	15,270
Due after 10 years - Amortized Cost		61,185	68,755
Due after 10 years - Carrying Value	[2]	61,185	68,755
Due after 10 years - Fair Value		51,375	65,046
Amortized Cost		79,680	87,250
Carrying Value	[2]	79,680	87,250
Fair Value		69,361	83,405
MBS [Member]
Debt Securities, Held-to-maturity, Maturity [Abstract]
Amortized Cost	[1],[4]	653,967	859,892
Carrying Value	[2],[4]	597,208	783,857
Fair Value	[4]	$ 664,609	$ 952,005

[1] Amortized cost of held-to-maturity securities includes adjustments made to the cost basis of an investment for accretion, amortization, and collection of cash. Amortized cost excludes accrued interest receivable of $1.6 million and $2.0 million at March 31, 2020, and December 31, 2019.

[2] 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 and the allowance for credit losses.

[3] Fair values of held-to-maturity securities were $733,970 and $1,035,410 at March 31, 2020, and December 31, 2019, respectively.

[4] 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.