Income Taxes - Significant Components of Temporary Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets:
Allowance for loan losses	$ 13,798	$ 13,463
Net unrealized losses on securities available-for-sale	0	1,091
Other employee benefits	3,039	2,712
Low income housing partnerships	3,494	3,249
Net adjustment to funded status of pension	5,438	5,173
Lease liabilities	11,257
State net operating loss carryforwards	5,134	4,573
Other	1,856	2,856
Gross Deferred Tax Assets	44,016	33,117
Less: Valuation allowance	(5,134)	(4,573)
Total Deferred Tax Assets	38,882	28,544
Deferred Tax Liabilities:
Net unrealized gains on securities available-for-sale	(2,570)	0
Prepaid pension	(5,971)	(6,164)
Deferred loan income	(3,555)	(3,219)
Purchase accounting adjustments	(1,269)	(100)
Depreciation on premises and equipment	(592)	(477)
Right-of-use lease assets	(10,476)
Other	(1,243)	(1,375)
Total Deferred Tax liabilities	(25,676)	(11,335)
Net Deferred Tax Asset	$ 13,206	$ 17,209