Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Allowance for loan losses	$ 13,251	$ 12,584
Post retirement benefit	3,720	3,414
Deferred compensation	2,228	1,939
Depreciation	1,042	949
Retirement income maintenance plan	1,602	1,455
ESOP	128	0
Stock-based compensation	35	0
Reserve for uncollected interest	24	62
Net unrealized losses on securities and defined benefit plans	19,060	18,221
State NOL	2,063	2,476
Alternative minimum assessment carryforwards	2,156	2,156
Charitable contribution carryforward	6,085	0
Other items	670	1,595
Gross deferred tax assets	52,064	44,851
Valuation allowance	(2,388)	(2,786)
Total deferred tax assets, net	49,676	42,065
Deferred tax liabilities:
Pension expense	26,071	26,234
Deferred loan costs	5,736	4,257
Intangible assets	1,621	1,642
Other items	34	48
Total gross deferred tax liabilities	33,462	32,181
Net deferred tax asset	$ 16,214	$ 9,884