Securities Available for sale, Unrealized Loss Position, Fair Value (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Available for sale, Unrealized Loss Position [Line Items]
Available for sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	203	490
Available for sale, Securities in Unrealized Loss Position, Less than 12 Months [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 2,182,644	$ 700,064
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	897,351	5,631,803
Available for sale securities, Unrealized Loss Position, Fair Value	3,079,995	6,331,867
Available for sale securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10,928	1,615
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9,358	136,642
Available for sale securities, Unrealized Loss Position, Accumulated Loss	20,286	138,257
Other than Temporary Impairment Loss, Available for sale, Recognized in Earnings	0	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 36,000	$ 45,000
U.S. Treasury [Member]
Available for sale, Unrealized Loss Position [Line Items]
Available for sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		1
Available for sale, Securities in Unrealized Loss Position, Less than 12 Months [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		$ 0
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value		493
Available for sale securities, Unrealized Loss Position, Fair Value		493
Available for sale securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		3
Available for sale securities, Unrealized Loss Position, Accumulated Loss		$ 3
Residential agency mortgage-backed securities [Member]
Available for sale, Unrealized Loss Position [Line Items]
Available for sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	133	289
Available for sale, Securities in Unrealized Loss Position, Less than 12 Months [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 1,352,597	$ 510,824
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	686,002	3,641,370
Available for sale securities, Unrealized Loss Position, Fair Value	2,038,599	4,152,194
Available for sale securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,690	1,158
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8,423	96,606
Available for sale securities, Unrealized Loss Position, Accumulated Loss	$ 15,113	$ 97,764
Commercial agency mortgage-backed securities [Member]
Available for sale, Unrealized Loss Position [Line Items]
Available for sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	69	197
Available for sale, Securities in Unrealized Loss Position, Less than 12 Months [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 830,047	$ 179,258
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	210,877	1,969,504
Available for sale securities, Unrealized Loss Position, Fair Value	1,040,924	2,148,762
Available for sale securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,238	394
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	907	39,969
Available for sale securities, Unrealized Loss Position, Accumulated Loss	$ 5,145	$ 40,363
Other debt securities [Member]
Available for sale, Unrealized Loss Position [Line Items]
Available for sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1	3
Available for sale, Securities in Unrealized Loss Position, Less than 12 Months [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 0	$ 9,982
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	472	20,436
Available for sale securities, Unrealized Loss Position, Fair Value	472	30,418
Available for sale securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]
Available for sale securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	63
Available for sale securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	28	64
Available for sale securities, Unrealized Loss Position, Accumulated Loss	$ 28	$ 127

Available-for-sale Securities, Securities in Unrealized Loss Position, Accumulated Loss [Abstract]

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Available-for-sale, Securities in Unrealized Loss Position, Fair Value [Abstract] [Abstract]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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