Summary of Significant Accounting Policies - Federal Home Loan Bank stock (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
OTTI losses, FHLB stock	$ 0	$ 0
Federal Home Loan Bank of Des Moines \| Common equity tier 1 capital
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank stock, minimum investment requirement	6,000,000	6,900,000
OTTI losses, FHLB stock	$ 0	$ 0

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration