Investment Securities, Part II (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) securities	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 141,581,000
After 1 through 5 years	397,120,000
After 5 through 10 years	76,611,000
After ten years	2,489,000
Fair Value	$ 617,801,000		$ 686,048,000
Available-for-sale, Weighted Average Yield, Maturities Year One (in hundredths)	2.42%
Available-for-sale , Weighted Average Yield, Maturities After 1 through 5 Years (in hundredths)	2.67%
Available-for-sale, Weighted Average Yield, Maturities After 5 through 10 Years (in hundredths)	2.93%
Available-for-sale , Weighted Average Yield, Maturities After 10 Years (in hundredths)	2.88%
Available-for-sale , Weighted Average Yield, Maturities (in hundredths)	2.65%
Available-for-sale, Full Tax-equivalent Yield, Maturities Year One (in hundredths)	2.63%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 1 through 5 Years (in hundredths)	2.87%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 5 through 10 years (in hundredths)	3.93%
Available-for-sale, Full Tax-equivalent Yield, Maturities After Ten Years (in hundredths)	3.79%
Available-for-sale, Full Tax-equivalent Yield, Maturities (in hundredths)	2.96%
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Debt Securities, Held-to-maturity	$ 24,563,000		69,542,000
Held To Maturity Weighted Average Yield Maturities Year One	1.93%
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	1.96%
Held To Maturity Tax Equivalent Yield Maturities Year One	1.93%
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	1.96%
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, Qualitative Disclosure [Abstract]
Less than 12 months, Fair Value	$ 177,861,000		93,924,000
Less than 12 months, Unrealized Losses	(4,354,000)		(398,000)
12 months or longer, Fair Value	3,679,000		21,235,000
12 months or longer, Unrealized losses	(85,000)		(191,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	181,540,000		115,159,000
Total Unrealized Losses	4,439,000		589,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	4,439,000		589,000
Credit losses on trust preferred securities held [Abstract]
Debt and Equity Securities, Gain (Loss)	531,000	$ 54,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Restricted	582,000,000		688,000,000
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	41,026,000
After 1 through 5 years	15,663,000
After 5 through 10 years	0
After ten years	0
Fair Value	56,689,000		107,320,000
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	19,536,000
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	5,027,000
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	24,563,000		69,542,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, Fair Value	5,802,000		23,375,000
Less than 12 months, Unrealized Losses	(94,000)		(60,000)
12 months or longer, Fair Value	0		0
12 months or longer, Unrealized losses	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	5,802,000		23,375,000
Total Unrealized Losses	94,000		60,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	94,000		60,000
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			14,996,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss			(25,000)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value			24,565,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss			(44,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value			39,561,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss			$ (69,000)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities			4
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	26,677,000
After 1 through 5 years	69,512,000
After 5 through 10 years	65,164,000
After ten years	2,149,000
Fair Value	163,502,000		$ 178,433,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, Fair Value	119,614,000		3,469,000
Less than 12 months, Unrealized Losses	(3,904,000)		(16,000)
12 months or longer, Fair Value	0		347,000
12 months or longer, Unrealized losses	0		(1,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	119,614,000		3,816,000
Total Unrealized Losses	3,904,000		$ 17,000
Number of securities in Unrealized Loss Positions | securities			1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,904,000		$ 17,000
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			347,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss			(1,000)
Mortgage-backed securities: GSE residential
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	73,878,000
After 1 through 5 years	310,186,000
After 5 through 10 years	11,447,000
After ten years	0
Fair Value	395,511,000		396,126,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, Fair Value	51,736,000		67,080,000
Less than 12 months, Unrealized Losses	(315,000)		(322,000)
12 months or longer, Fair Value	3,679,000		20,888,000
12 months or longer, Unrealized losses	(85,000)		(190,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	55,415,000		87,968,000
Total Unrealized Losses	$ 400,000		$ 512,000
Number of securities in Unrealized Loss Positions | securities	5		14
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 400,000		$ 512,000
Other securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	0
After 1 through 5 years	1,759,000
After 5 through 10 years	0
After ten years	340,000
Fair Value	2,099,000		4,169,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, Fair Value	709,000
Less than 12 months, Unrealized Losses	(41,000)
12 months or longer, Fair Value	0
12 months or longer, Unrealized losses	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	709,000
Total Unrealized Losses	41,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 41,000		$ 0