Investments Available-for-Sale Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	$ 2,937,195	$ 2,013,102
Less than 12 Months - Unrealized Losses	(89,508)	(15,802)
12 Months or More - Fair Value	1,709,103	3,047,211
12 Months or More - Unrealized Losses	(105,367)	(66,552)
Total - Fair Value	4,646,298	5,060,313
Total - Unrealized Losses	(194,875)	(82,354)
HFA securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	12,497	12,229
Less than 12 Months - Unrealized Losses	(1,323)	(1,591)
12 Months or More - Fair Value	45,298	52,423
12 Months or More - Unrealized Losses	(2,602)	(3,077)
Total - Fair Value	57,795	64,652
Total - Unrealized Losses	(3,925)	(4,668)
Supranational institutions [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	0	0
Less than 12 Months - Unrealized Losses	0	0
12 Months or More - Fair Value	438,284	416,429
12 Months or More - Unrealized Losses	(19,437)	(12,925)
Total - Fair Value	438,284	416,429
Total - Unrealized Losses	(19,437)	(12,925)
U.S. government-owned corporations [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	0	0
Less than 12 Months - Unrealized Losses	0	0
12 Months or More - Fair Value	314,724	296,761
12 Months or More - Unrealized Losses	(61,987)	(26,431)
Total - Fair Value	314,724	296,761
Total - Unrealized Losses	(61,987)	(26,431)
GSE [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	0	0
Less than 12 Months - Unrealized Losses	0	0
12 Months or More - Fair Value	133,789	123,786
12 Months or More - Unrealized Losses	(15,279)	(7,149)
Total - Fair Value	133,789	123,786
Total - Unrealized Losses	(15,279)	(7,149)
Other Than MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	12,497	12,229
Less than 12 Months - Unrealized Losses	(1,323)	(1,591)
12 Months or More - Fair Value	932,095	889,399
12 Months or More - Unrealized Losses	(99,305)	(49,582)
Total - Fair Value	944,592	901,628
Total - Unrealized Losses	(100,628)	(51,173)
U.S. government-guaranteed - single-family MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	1,294	10,885
Less than 12 Months - Unrealized Losses	(8)	(1)
12 Months or More - Fair Value	51,292	45,490
12 Months or More - Unrealized Losses	(226)	(2,288)
Total - Fair Value	52,586	56,375
Total - Unrealized Losses	(234)	(2,289)
U.S. government-guaranteed - multifamily MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	0	0
Less than 12 Months - Unrealized Losses	0	0
12 Months or More - Fair Value	39,735	282,617
12 Months or More - Unrealized Losses	(15)	(1,057)
Total - Fair Value	39,735	282,617
Total - Unrealized Losses	(15)	(1,057)
MBS [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	2,924,698	2,000,873
Less than 12 Months - Unrealized Losses	(88,185)	(14,211)
12 Months or More - Fair Value	777,008	2,157,812
12 Months or More - Unrealized Losses	(6,062)	(16,970)
Total - Fair Value	3,701,706	4,158,685
Total - Unrealized Losses	(94,247)	(31,181)
GSE - single-family [Member] | Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	126,722	189,402
Less than 12 Months - Unrealized Losses	(605)	(968)
12 Months or More - Fair Value	397,329	1,423,927
12 Months or More - Unrealized Losses	(2,517)	(12,409)
Total - Fair Value	524,051	1,613,329
Total - Unrealized Losses	(3,122)	(13,377)
GSE - multifamily [Member] | Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 Months - Fair Value	2,796,682	1,800,586
Less than 12 Months - Unrealized Losses	(87,572)	(13,242)
12 Months or More - Fair Value	288,652	405,778
12 Months or More - Unrealized Losses	(3,304)	(1,216)
Total - Fair Value	3,085,334	2,206,364
Total - Unrealized Losses	$ (90,876)	$ (14,458)