Investment Securities, Part II (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) securities	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) securities
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 95,422,000
After 1 through 5 years	336,675,000
After 5 through 10 years	184,565,000
After ten years	4,542,000
Fair Value	$ 621,204,000		$ 619,848,000
Available-for-sale, Weighted Average Yield, Maturities Year One (in hundredths)	2.23%
Available-for-sale , Weighted Average Yield, Maturities After 1 through 5 Years (in hundredths)	2.56%
Available-for-sale, Weighted Average Yield, Maturities After 5 through 10 Years (in hundredths)	2.68%
Available-for-sale , Weighted Average Yield, Maturities After 10 Years (in hundredths)	2.57%
Available-for-sale , Weighted Average Yield, Maturities (in hundredths)	2.55%
Available-for-sale, Full Tax-equivalent Yield, Maturities Year One (in hundredths)	2.65%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 1 through 5 Years (in hundredths)	3.02%
Available-for-sale, Full Tax-equivalent Yield, Maturities After 5 through 10 years (in hundredths)	3.47%
Available-for-sale, Full Tax-equivalent Yield, Maturities After Ten Years (in hundredths)	3.41%
Available-for-sale, Full Tax-equivalent Yield, Maturities (in hundredths)	3.10%
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities	$ 69,306,000		74,231,000
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)	35.00%
Percentage investment book value exceeds total stockholders' equity (in hundredths)	10.00%
Investment Securities Pledged as Collateral	$ 463,000,000		509,000,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	185,129,000		484,981,000
Less than 12 months, Unrealized Losses	(2,093,000)		(9,411,000)
12 months or longer, Fair Value	22,127,000		9,525,000
12 months or longer, Unrealized losses	(700,000)		(1,673,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	207,256,000		494,506,000
Total Unrealized Losses	2,793,000		11,084,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 2,793,000		11,084,000
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	2,933,000
Fair Value	2,701,000
Unrealized Gains (Losses)	(232,000)
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	75,846,000
After 1 through 5 years	39,439,000
After 5 through 10 years	11,116,000
After ten years	0
Fair Value	126,401,000		136,324,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	39,993,000
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	29,313,000
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	69,306,000		74,231,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	73,135,000		125,257,000
Less than 12 months, Unrealized Losses	(1,009,000)		(2,508,000)
12 months or longer, Fair Value	1,003,000		0
12 months or longer, Unrealized losses	(5,000)		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	74,138,000		125,257,000
Total Unrealized Losses	1,014,000		2,508,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,014,000		2,508,000
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	29,336,000		53,295,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(229,000)		(1,338,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	14,725,000		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(268,000)		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	44,061,000		53,295,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(497,000)		(1,338,000)
Obligations of states and political subdivisions
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	19,153,000
After 1 through 5 years	81,336,000
After 5 through 10 years	70,371,000
After ten years	1,666,000
Fair Value	172,526,000		162,705,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	25,250,000		93,405,000
Less than 12 months, Unrealized Losses	(274,000)		(2,804,000)
12 months or longer, Fair Value	9,339,000		0
12 months or longer, Unrealized losses	(212,000)		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	34,589,000		93,405,000
Total Unrealized Losses	486,000		2,804,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	486,000		2,804,000
Mortgage-backed securities: GSE residential
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	423,000
After 1 through 5 years	213,894,000
After 5 through 10 years	101,040,000
After ten years	0
Fair Value	315,357,000		314,991,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	86,744,000		266,319,000
Less than 12 months, Unrealized Losses	(810,000)		(4,099,000)
12 months or longer, Fair Value	9,084,000		5,878,000
12 months or longer, Unrealized losses	(251,000)		(270,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	95,828,000		272,197,000
Total Unrealized Losses	$ 1,061,000		$ 4,369,000
Number of securities in Unrealized Loss Positions | securities	5		2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1,061,000		$ 4,369,000
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	2,701,000
Fair Value	2,701,000		1,652,000
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	2,701,000		1,652,000
12 months or longer, Unrealized losses	(232,000)		(1,398,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,701,000		1,652,000
Total Unrealized Losses	$ 232,000		$ 1,398,000
Number of securities in Unrealized Loss Positions | securities	1		1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 232,000		$ 1,398,000
Other securities
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	0
After 1 through 5 years	2,006,000
After 5 through 10 years	2,038,000
After ten years	175,000
Fair Value	4,219,000		4,176,000
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		1,995,000
12 months or longer, Unrealized losses	0		(5,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	0		1,995,000
Total Unrealized Losses	0		$ 5,000
Number of securities in Unrealized Loss Positions | securities			1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0		$ 5,000