Mortgage Loans Held for Portfolio Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Allowance for credit losses - mortgage loans held for portfolio	$ 3,500	$ 500
US Government Agency Insured Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Allowance for credit losses - mortgage loans held for portfolio	$ 0	$ 0

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant