Federal Home Loan Bank of Boston Stock - Additional Information (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Federal Home Loan Bank Stock [Line Items]
Federal Home Loan Bank of Boston Stock, at cost	$ 7,854,000	$ 6,844,000
Federal Home Loan Bank of Boston
Federal Home Loan Bank Stock [Line Items]
Federal Home Loan Bank of Boston Stock, at cost	7,900,000	6,800,000
Impairment on investment of federal home loan bank stock	$ 0	$ 0