Income Taxes - Summary of Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Gross deferred tax assets
Allowance for loan losses	$ 5,029	$ 4,715
Accrued retirement benefits	1,592	2,082
Unrealized losses on AFS securities	171	957
Incentive compensation	1,248	1,189
Equity based compensation	1,034	849
Lease Liability	9,765	333
ESOP dividends	165	169
Loss carryforwards as a result of the Optima merger	877
Intangibles (merger related)	472
Other	252	155
Total gross deferred tax assets	20,605	10,449
Gross deferred tax liabilities
Deferred loan origination costs	(911)	(459)
Depreciation of premises and equipment	(1,021)	(678)
Right of Use Asset	(9,356)
Mortgage servicing rights	(368)	(187)
Goodwill	(113)	(114)
Derivative transactions	(607)	(294)
Total gross deferred tax liabilities	(12,376)	(1,732)
Net deferred tax asset	$ 8,229	$ 8,717