Deposits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deposit amount
Non-interest bearing	$ 54,927,000	$ 51,744,000
Savings accounts	908,175,000	991,310,000
Certificates of deposit	463,943,000	391,141,000
Money market	4,917,000	5,291,000
Checking and Super NOW	199,971,000	189,678,000
Total	$ 1,631,933,000	$ 1,629,164,000
Interest rate
Savings accounts (as a percent)	0.49%	0.50%
Certificates of deposit (as a percent)	1.87%	1.89%
Money market (as a percent)	0.45%	0.44%
Checking and Super NOW (as a percent)	0.02%	0.02%
Total (as a percent)	0.81%	0.77%
Maturity of certificate of deposit accounts
2019	$ 310,465,000
2020	88,002,000
2021	38,394,000
2022	14,666,000
2023	12,416,000
Total	463,943,000	$ 391,141,000
Deposit with balances greater than or equal to $250,000
Maximum amount of account owner deposit in bank insured by FDIC	250,000
Interest expense by type of deposit
Savings	4,593,000	4,842,000
Certificates of deposit and money market	8,829,000	6,134,000
Checking and Super NOW	41,000	39,000
Total	13,463,000	11,015,000
Overdrawn deposit accounts reclassified as loans	37,000	34,000
Domestic
Deposit with balances greater than or equal to $250,000
Total	$ 272,700,000	$ 244,600,000