Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Defined postretirement benefit obligation	$ 7,877,000	$ 8,385,000
Allowance for loan losses	7,697,000	5,671,000
Federal net operating loss carryforwards	5,093,000	650,000
Securities available-for-sale	2,184,000	400,000
California net operating loss carryforwards	2,128,000	394,000
Accrued expenses	1,939,000	910,000
Stock compensation	1,244,000	1,272,000
State income taxes	1,117,000	975,000
Premises and equipment	642,000	649,000
Split-dollar life insurance benefit plan	80,000	76,000
Tax credit carryforwards	71,000	70,000
Nonaccrual interest	55,000	76,000
Other	716,000	365,000
Total deferred tax assets	30,843,000	19,893,000
Deferred tax liabilities:
Intangible liabilities	(1,671,000)	(1,357,000)
Loan fees	(1,089,000)	(1,079,000)
Prepaid expenses	(554,000)	(533,000)
I/O strips	(163,000)	(406,000)
FHLB stock	(174,000)	(171,000)
Other	(103,000)	(100,000)
Total deferred tax liabilities	(3,754,000)	(3,646,000)
Net deferred tax assets	$ 27,089,000	$ 16,247,000