Mortgage Loans Held for Portfolio (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Par Value		$ 4,462,014	$ 4,432,458
Premiums		66,933	66,776
Discounts		(1,535)	(1,607)
Deferred derivative gains, net		4,562	4,124
Total mortgage loans held for portfolio	[1]	4,531,974	4,501,751
Less: allowance for credit losses		(3,500)	(500)
Total mortgage loans, net of allowance for credit losses		4,528,474	4,501,251
Real Estate Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans held for portfolio - accrued interest receivable		$ 23,500	23,500
Fixed-rate 15-year single-family mortgages
Loans and Leases Receivable Disclosure [Line Items]
Original contractual terms		15 years
Fixed-rate 15-year single-family mortgages | GSE - single-family [Member]
Loans and Leases Receivable Disclosure [Line Items]
Par Value		$ 327,700	339,042
Fixed-rate 20- and 30-year single-family mortgages | GSE - single-family [Member]
Loans and Leases Receivable Disclosure [Line Items]
Par Value		$ 4,134,314	$ 4,093,416
Minimum [Member] | Fixed-rate 20- and 30-year single-family mortgages
Loans and Leases Receivable Disclosure [Line Items]
Original contractual terms		20 years
Maximum [Member] | Fixed-rate 20- and 30-year single-family mortgages
Loans and Leases Receivable Disclosure [Line Items]
Original contractual terms		30 years

[1] Excludes accrued interest receivable of $23.5 million at both March 31, 2020, and December 31, 2019