Investment Securities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Available-for-sale: [Abstract]
Amortized Cost	$ 693,854,000		$ 701,225,000
Gross Unrealized Gains	5,347,000		2,310,000
Gross Unrealized (Losses)	(3,583,000)		(11,261,000)
Fair Value	695,618,000		692,274,000
Debt and Equity Securities, Gain (Loss)	54,000	$ 20,000
Held-to-maturity: [Abstract]
Debt Securities, Held-to-maturity	69,462,000		69,436,000
Debt Securities, Held-to-maturity, Fair Value	68,743,000		67,909,000
Realized Investment Gains (Losses) [Abstract]
Gross gains	84,000	20,000
Gross losses	(30,000)	$ 0
U.S. Treasury securities and obligations of U.S. government corporations & agencies
Available-for-sale: [Abstract]
Amortized Cost	190,845,000		201,380,000
Gross Unrealized Gains	926,000		504,000
Gross Unrealized (Losses)	(1,044,000)		(3,235,000)
Fair Value	190,727,000		198,649,000
Held-to-maturity: [Abstract]
Debt Securities, Held-to-maturity	69,462,000		69,436,000
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	11,000		0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(730,000)		(1,527,000)
Debt Securities, Held-to-maturity, Fair Value	68,743,000		67,909,000
Obligations of states and political subdivisions
Available-for-sale: [Abstract]
Amortized Cost	188,572,000		193,195,000
Gross Unrealized Gains	2,996,000		1,224,000
Gross Unrealized (Losses)	(465,000)		(1,840,000)
Fair Value	191,103,000		192,579,000
Mortgage-backed securities: GSE residential
Available-for-sale: [Abstract]
Amortized Cost	312,159,000		304,372,000
Gross Unrealized Gains	1,399,000		486,000
Gross Unrealized (Losses)	(2,074,000)		(6,186,000)
Fair Value	311,484,000		298,672,000
Trust preferred securities
Available-for-sale: [Abstract]
Debt and Equity Securities, Gain (Loss)	846,000
Other securities
Available-for-sale: [Abstract]
Amortized Cost	2,278,000		2,278,000
Gross Unrealized Gains	26,000		96,000
Gross Unrealized (Losses)	0		0
Fair Value	$ 2,304,000		$ 2,374,000