Income Taxes - Temporary differences (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Allowance for loan losses	$ 2,286	$ 2,482
Unrealized loss on available‑for‑sale securities	442	429
State tax	421	330
Other	105	470
Total assets	3,254	3,711
Deferred tax liabilities
Depreciation	(152)	(272)
Mortgage ‑ servicing rights	(16,037)	(19,009)
Other		(37)
Total liabilities	(16,189)	(19,318)
Total liabilities	$ (12,935)	$ (15,607)