Investment Securities, Part II (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) securities	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) securities
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 98,512,000
After 1 through 5 years	219,205,000
After 5 through 10 years	72,582,000
After ten years	179,563,000
Fair Value	$ 569,862,000		$ 578,579,000
Available-for-sale, Weighted Average Yield, Maturities Year One (in hundredths)	2.31%
Available-for-sale , Weighted Average Yield, Maturities After 1 through 5 Years (in hundredths)	2.66%
Available-for-sale, Weighted Average Yield, Maturities After 5 through 10 Years (in hundredths)	3.05%
Available-for-sale , Weighted Average Yield, Maturities After 10 Years (in hundredths)	2.82%
Available-for-sale , Weighted Average Yield, Maturities (in hundredths)	2.70%
Available-for-sale, Full Tax-equivalent Yield, Maturities Year One (in hundredths)	2.47%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 1 through 5 Years (in hundredths)	3.01%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 5 through 10 years (in hundredths)	4.22%
Available-for-sale, Full Tax-equivalent Yield, Maturities After Ten Years (in hundredths)	2.83%
Available-for-sale, Full Tax-equivalent Yield, Maturities (in hundredths)	3.01%
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities	$ 69,358,000		69,332,000
Held To Maturity Weighted Average Yield Maturities Year One	1.76%
Held To Maturity Weighted Average Yield Maturities After 1 Through 5 Years	2.08%
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	1.76%
Held To Maturity Tax Equivalent Yield Maturities After 1 Through 5 Years	2.08%
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%
Investment Securities Pledged as Collateral	$ 496,000,000		479,000,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	345,485,000		289,151,000
Less than 12 months, Unrealized Losses	(6,909,000)		(3,251,000)
12 months or longer, Fair Value	130,915,000		82,396,000
12 months or longer, Unrealized losses	(6,095,000)		(2,613,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	476,400,000		371,547,000
Total Unrealized Losses	13,004,000		5,864,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 13,004,000		5,864,000
Details of Trust Preferred Securities [Abstract]
Coupon Rate of Trust Preferred Security	floating rate coupon of 3-month LIBOR plus 90 basis points
Number of Ratios Utilized in OTTI Credit Model	29
OTTI Cash Flow Initial Default Rate	2.00%
Period For Initial Default Rate Used In OTTI Analysis	two years
Default Rate Applied For Remainder Of OTTI Analysis	36 basis points
Recovery Rate Used In OTTI Cash Flow Analysis	10.00%
Credit losses on trust preferred securities held [Abstract]
Beginning of period	$ 1,111,000	$ 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	1,111,000	$ 1,111,000
PreTSL XXVIII [Member]
Details of Trust Preferred Securities [Abstract]
Book Value	2,849,000
Fair Value	2,522,000
Unrealized Gains (Losses)	(327,000)
Other-than- temporary Impairment Recorded To-date	(1,111,000)
U.S. Treasury securities and obligations of U.S. government corporations & agencies
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	83,291,000
After 1 through 5 years	37,794,000
After 5 through 10 years	0
After ten years	0
Fair Value	121,085,000		113,770,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	39,994,000
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	29,364,000
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	0
Held-to-maturity Securities	69,358,000		69,332,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	68,712,000		58,584,000
Less than 12 months, Unrealized Losses	(1,639,000)		(540,000)
12 months or longer, Fair Value	47,373,000		47,972,000
12 months or longer, Unrealized losses	(2,095,000)		(1,494,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	116,085,000		106,556,000
Total Unrealized Losses	$ 3,734,000		$ 2,034,000
Number of securities in Unrealized Loss Positions | securities	11		11
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 3,734,000		$ 2,034,000
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	24,554,000		34,101,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(313,000)		(525,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	38,137,000		14,540,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,422,000)		(453,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	62,691,000		48,641,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,735,000)		$ (978,000)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	7		7
Obligations of states and political subdivisions
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 15,213,000
After 1 through 5 years	70,993,000
After 5 through 10 years	72,582,000
After ten years	1,437,000
Fair Value	160,225,000		$ 166,266,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	66,996,000		42,618,000
Less than 12 months, Unrealized Losses	(1,346,000)		(769,000)
12 months or longer, Fair Value	14,901,000		9,267,000
12 months or longer, Unrealized losses	(882,000)		(256,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	81,897,000		51,885,000
Total Unrealized Losses	$ 2,228,000		$ 1,025,000
Number of securities in Unrealized Loss Positions | securities	33		39
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 2,228,000		$ 1,025,000
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	14,901,000		9,267,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(882,000)		(256,000)
Mortgage-backed securities: GSE residential
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	8,000
After 1 through 5 years	108,417,000
After 5 through 10 years	0
After ten years	175,412,000
Fair Value	283,837,000		293,811,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	209,777,000		187,949,000
Less than 12 months, Unrealized Losses	(3,924,000)		(1,942,000)
12 months or longer, Fair Value	66,119,000		22,609,000
12 months or longer, Unrealized losses	(2,791,000)		(518,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	275,896,000		210,558,000
Total Unrealized Losses	$ 6,715,000		$ 2,460,000
Number of securities in Unrealized Loss Positions | securities	27		26
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 6,715,000		$ 2,460,000
Trust preferred securities
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	0
After 1 through 5 years	0
After 5 through 10 years	0
After ten years	2,522,000
Fair Value	2,522,000		2,548,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	0		0
Less than 12 months, Unrealized Losses	0		0
12 months or longer, Fair Value	2,522,000		2,548,000
12 months or longer, Unrealized losses	(327,000)		(345,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,522,000		2,548,000
Total Unrealized Losses	$ 327,000		$ 345,000
Number of securities in Unrealized Loss Positions | securities	1		1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 327,000		$ 345,000
Other securities
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	0
After 1 through 5 years	2,001,000
After 5 through 10 years	0
After ten years	192,000
Fair Value	2,193,000		2,184,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	0		0
Less than 12 months, Unrealized Losses	0		0
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	0		0
Total Unrealized Losses	0		0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0		$ 0