Investment Securities, Part II (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) securities	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 175,644,000
After 1 through 5 years	344,695,000
After 5 through 10 years	174,040,000
After ten years	1,239,000
Fair Value	$ 695,618,000		$ 692,274,000
Available-for-sale, Weighted Average Yield, Maturities Year One (in hundredths)	2.64%
Available-for-sale , Weighted Average Yield, Maturities After 1 through 5 Years (in hundredths)	2.85%
Available-for-sale, Weighted Average Yield, Maturities After 5 through 10 Years (in hundredths)	2.92%
Available-for-sale , Weighted Average Yield, Maturities After 10 Years (in hundredths)	3.06%
Available-for-sale , Weighted Average Yield, Maturities (in hundredths)	2.82%
Available-for-sale, Full Tax-equivalent Yield, Maturities Year One (in hundredths)	2.79%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 1 through 5 Years (in hundredths)	3.12%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 5 through 10 years (in hundredths)	3.43%
Available-for-sale, Full Tax-equivalent Yield, Maturities After Ten Years (in hundredths)	4.07%
Available-for-sale, Full Tax-equivalent Yield, Maturities (in hundredths)	3.12%
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Debt Securities, Held-to-maturity	$ 69,462,000		69,436,000
Held To Maturity Weighted Average Yield Maturities Year One	1.83%
Held To Maturity Weighted Average Yield Maturities After 1 Through 5 Years	2.06%
Held To Maturity Weighted Average Yield Maturities After 5 Through 10 Years	0.00%
Held To Maturity Weighted Average Yield Maturities After 10 Years	0.00%
Held To Maturity Weighted Average Yield Maturities	1.90%
Held To Maturity Tax Equivalent Yield Maturities Year One	1.83%
Held To Maturity Tax Equivalent Yield Maturities After 1 Through 5 Years	2.06%
Held To Maturity Tax Equivalent Yield Maturities After 5 Through 10 Years	0.00%
Held To Maturity Tax Equivalent Yield Maturities After 10 Years	0.00%
Held To Maturity Tax Equivalent Yield Maturities	1.90%
Tax rate used to calculate tax-equivalent yields (in hundredths)	21.00%
Percentage investment book value exceeds total stockholders' equity (in hundredths)	10.00%
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	$ 4,332,000		136,312,000
Less than 12 months, Unrealized Losses	(8,000)		(1,748,000)
12 months or longer, Fair Value	312,533,000		319,611,000
12 months or longer, Unrealized losses	(3,575,000)		(9,513,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	316,865,000		455,923,000
Total Unrealized Losses	3,583,000		11,261,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,583,000		11,261,000
Credit losses on trust preferred securities held [Abstract]
Beginning of period	0	$ 1,111,000
Additions related to OTTI losses not previously recognized	0	0
Reductions due to sales / (recoveries)	0	0
Reductions due to change in intent or likelihood of sale	0	0
Additions related to increases in previously recognized OTTI losses	0	0
Reductions due to increases in expected cash flows	0	0
End of period	0	1,111,000
Debt and Equity Securities, Gain (Loss)	54,000	$ 20,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Restricted	574,000,000		628,000,000
U.S. Treasury securities and obligations of U.S. government corporations & agencies
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	148,125,000
After 1 through 5 years	42,602,000
After 5 through 10 years	0
After ten years	0
Fair Value	190,727,000		198,649,000
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	49,940,000
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	19,522,000
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Amortized Cost	0
Debt Securities, Held-to-maturity	69,462,000		69,436,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	998,000		16,095,000
Less than 12 months, Unrealized Losses	0		(148,000)
12 months or longer, Fair Value	82,772,000		105,549,000
12 months or longer, Unrealized losses	(1,044,000)		(3,087,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	83,770,000		121,644,000
Total Unrealized Losses	$ 1,044,000		$ 3,235,000
Number of securities in Unrealized Loss Positions | securities	19		23
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1,044,000		$ 3,235,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0		19,683,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0		(147,000)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	63,775,000		48,226,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(730,000)		(1,380,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	63,775,000		67,909,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	$ (730,000)		$ (1,527,000)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	13		9
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 26,862,000
After 1 through 5 years	85,494,000
After 5 through 10 years	77,798,000
After ten years	949,000
Fair Value	191,103,000		$ 192,579,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	1,382,000		38,782,000
Less than 12 months, Unrealized Losses	(3,000)		(450,000)
12 months or longer, Fair Value	30,225,000		42,741,000
12 months or longer, Unrealized losses	(462,000)		(1,390,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	31,607,000		81,523,000
Total Unrealized Losses	$ 465,000		$ 1,840,000
Number of securities in Unrealized Loss Positions | securities	61		84
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 465,000		$ 1,840,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	30,225,000		42,741,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(462,000)		(1,390,000)
Mortgage-backed securities: GSE residential
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	657,000
After 1 through 5 years	214,585,000
After 5 through 10 years	96,242,000
After ten years	0
Fair Value	311,484,000		298,672,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	1,952,000		81,435,000
Less than 12 months, Unrealized Losses	(5,000)		(1,150,000)
12 months or longer, Fair Value	199,536,000		171,321,000
12 months or longer, Unrealized losses	(2,069,000)		(5,036,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	201,488,000		252,756,000
Total Unrealized Losses	$ 2,074,000		$ 6,186,000
Number of securities in Unrealized Loss Positions | securities	77		69
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 2,074,000		$ 6,186,000
Trust preferred securities
Credit losses on trust preferred securities held [Abstract]
Debt and Equity Securities, Gain (Loss)	846,000
Other securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	0
After 1 through 5 years	2,014,000
After 5 through 10 years	0
After ten years	290,000
Fair Value	2,304,000		2,374,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0		$ 0