Available-for-Sale Securities Redemption Terms (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	$ 7,482,922	$ 6,002,902
Available-for-sale securities Fair Value		7,409,000	5,849,944
Other Than Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost		7,600	0
Due in one year or less, fair value		7,563	0
Due after one year through five years, amortized cost		61,720	55,500
Due after one year through five years, fair value		57,089	49,601
Due after five years through 10 years, amortized cost		477,232	465,248
Due after five years through 10 years, fair value		463,465	450,102
Due after 10 years, amortized cost		406,249	374,126
Due after 10 years, fair value		373,511	343,849
Amortized Cost	[1]	952,801	894,874
Available-for-sale securities Fair Value		901,628	843,552
MBS [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	6,530,121	5,108,028
Available-for-sale securities Fair Value		6,507,372	5,006,392
Amortized Cost MBS	[2]	6,530,121	5,108,028
Fair Value MBS	[2]	$ 6,507,372	$ 5,006,392

[1] Amortized cost of available-for-sale securities includes adjustments made to the cost basis of an investment for accretion, amortization, collection of cash, and fair-value hedge accounting adjustments.

[2] 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 obligations with or without call or prepayment fees.