Investment Securities - Summary of Amortized Cost and Estimated Fair Value (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Securities available for sale
Amortized Cost	$ 303,845,000	$ 301,854,000
Unrealized Gains	859,000	1,872,000
Unrealized Losses	(4,532,000)	(3,310,000)
Fair Value (Estimated)	300,172,000	300,416,000
Securities to be held to maturity, cost and FMV [Abstract]
Amortized Cost	256,567,000	226,828,000
Unrealized Gains	4,499,000	2,973,000
Unrealized Losses	(1,411,000)	(4,264,000)
Fair Value (Estimated)	259,655,000	225,537,000
Restricted equity securities, cost and FMV [Abstract]
Amortized Cost	10,358,000	11,930,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value Estimated	10,358,000	11,930,000
Federal Home Loan Bank Stock
Restricted equity securities, cost and FMV [Abstract]
Amortized Cost	9,321,000	10,893,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value Estimated	9,321,000	10,893,000
Federal Reserve Bank Stock
Restricted equity securities, cost and FMV [Abstract]
Amortized Cost	1,037,000	1,037,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value Estimated	1,037,000	1,037,000
Mortgage-backed securities
Securities available for sale
Amortized Cost-Debt	293,689,000	282,397,000
Unrealized Gains	722,000	1,334,000
Unrealized Losses	(4,422,000)	(3,127,000)
Fair Value (Estimated)	289,989,000	280,604,000
State and political subdivisions
Securities available for sale
Amortized Cost-Debt	6,860,000	16,183,000
Unrealized Gains	16,000	475,000
Unrealized Losses	(107,000)	(176,000)
Fair Value (Estimated)	6,769,000	16,482,000
Other equity securities
Securities available for sale
Amortized Cost-Debt	3,296,000	3,274,000
Unrealized Gains	121,000	63,000
Unrealized Losses	(3,000)	(7,000)
Fair Value (Estimated)	3,414,000	3,330,000
U.S. Government-sponsored agencies
Securities to be held to maturity, cost and FMV [Abstract]
Amortized Cost	11,155,000	11,943,000
Unrealized Gains	0	35,000
Unrealized Losses	(180,000)	(233,000)
Fair Value (Estimated)	10,975,000	11,745,000
Mortgage-backed securities
Securities to be held to maturity, cost and FMV [Abstract]
Amortized Cost	23,284,000	31,201,000
Unrealized Gains	568,000	967,000
Unrealized Losses	(128,000)	(147,000)
Fair Value (Estimated)	23,724,000	32,021,000
State and political subdivisions
Securities to be held to maturity, cost and FMV [Abstract]
Amortized Cost	217,828,000	179,384,000
Unrealized Gains	3,931,000	1,971,000
Unrealized Losses	(1,103,000)	(3,884,000)
Fair Value (Estimated)	220,656,000	177,471,000
Corporate securities
Securities to be held to maturity, cost and FMV [Abstract]
Amortized Cost	4,300,000	4,300,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value (Estimated)	$ 4,300,000	$ 4,300,000

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