The yield on an available-for-sale government security, when the effect of reduced taxes are taken into account, for securities that mature. The full tax-equivalent yield show what yield a fully taxable security would have to give, in order to be equivalent to a tax free government security.

No definition available.

Investment Securities, Part II (Details)	3 Months Ended		9 Months Ended
Investment Securities, Part II (Details)	Sep. 30, 2018 USD ($) securities	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) securities	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 102,123,000		$ 102,123,000
After 1 through 5 years	238,893,000		238,893,000
After 5 through 10 years	256,635,000		256,635,000
After ten years	1,429,000		1,429,000
Fair Value	599,080,000		$ 599,080,000		$ 578,579,000
Available-for-sale, Weighted Average Yield, Maturities Year One (in hundredths)			2.34%
Available-for-sale , Weighted Average Yield, Maturities After 1 through 5 Years (in hundredths)			2.76%
Available-for-sale, Weighted Average Yield, Maturities After 5 through 10 Years (in hundredths)			2.95%
Available-for-sale , Weighted Average Yield, Maturities After 10 Years (in hundredths)			3.12%
Available-for-sale , Weighted Average Yield, Maturities (in hundredths)			2.77%
Available-for-sale, Full Tax-equivalent Yield, Maturities Year One (in hundredths)			2.51%
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)			3.31%
Available-for-sale, Full Tax-equivalent Yield, Maturities After Ten Years (in hundredths)			4.16%
Available-for-sale, Full Tax-equivalent Yield, Maturities (in hundredths)			3.10%
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Debt Securities, Held-to-maturity	69,409,000		$ 69,409,000		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%
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	403,312,000		$ 403,312,000		289,151,000
Less than 12 months, Unrealized Losses	(13,019,000)		(13,019,000)		(3,251,000)
12 months or longer, Fair Value	119,620,000		119,620,000		82,396,000
12 months or longer, Unrealized losses	(4,759,000)		(4,759,000)		(2,613,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	522,932,000		522,932,000		371,547,000
Total Unrealized Losses	17,778,000		17,778,000		5,864,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	17,778,000		17,778,000		5,864,000
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)			(1,111,000)	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	0	1,111,000
Debt and Equity Securities, Gain (Loss)	0	$ 254,000	901,000	$ 589,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Restricted	575,000,000		575,000,000		479,000,000
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	85,272,000		85,272,000
After 1 through 5 years	37,397,000		37,397,000
After 5 through 10 years	0		0
After ten years	0		0
Fair Value	122,669,000		122,669,000		113,770,000
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	39,994,000		39,994,000
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	29,415,000		29,415,000
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	0		0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Amortized Cost	0		0
Debt Securities, Held-to-maturity	69,409,000		69,409,000		69,332,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	67,162,000		67,162,000		58,584,000
Less than 12 months, Unrealized Losses	(1,957,000)		(1,957,000)		(540,000)
12 months or longer, Fair Value	55,507,000		55,507,000		47,972,000
12 months or longer, Unrealized losses	(2,739,000)		(2,739,000)		(1,494,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	122,669,000		122,669,000		106,556,000
Total Unrealized Losses	$ 4,696,000		$ 4,696,000		$ 2,034,000
Number of securities in Unrealized Loss Positions \| securities	14		14		11
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 4,696,000		$ 4,696,000		$ 2,034,000
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	24,510,000		24,510,000		34,101,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(340,000)		(340,000)		(525,000)
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	42,885,000		42,885,000		14,540,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,674,000)		(1,674,000)		(453,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	67,395,000		67,395,000		48,641,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	$ (2,014,000)		$ (2,014,000)		$ (978,000)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| securities	8		8		7
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	$ 16,847,000		$ 16,847,000
After 1 through 5 years	78,561,000		78,561,000
After 5 through 10 years	76,890,000		76,890,000
After ten years	1,048,000		1,048,000
Fair Value	173,346,000		173,346,000		$ 166,266,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	101,192,000		101,192,000		42,618,000
Less than 12 months, Unrealized Losses	(2,338,000)		(2,338,000)		(769,000)
12 months or longer, Fair Value	18,856,000		18,856,000		9,267,000
12 months or longer, Unrealized losses	(1,159,000)		(1,159,000)		(256,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	120,048,000		120,048,000		51,885,000
Total Unrealized Losses	$ 3,497,000		$ 3,497,000		$ 1,025,000
Number of securities in Unrealized Loss Positions \| securities	41		41		39
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 3,497,000		$ 3,497,000		$ 1,025,000
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	18,856,000		18,856,000		9,267,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,159,000)		(1,159,000)		(256,000)
Mortgage-backed securities: GSE residential
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
One year or less	4,000		4,000
After 1 through 5 years	120,920,000		120,920,000
After 5 through 10 years	179,745,000		179,745,000
After ten years	0		0
Fair Value	300,669,000		300,669,000		293,811,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value	234,958,000		234,958,000		187,949,000
Less than 12 months, Unrealized Losses	(8,724,000)		(8,724,000)		(1,942,000)
12 months or longer, Fair Value	45,257,000		45,257,000		22,609,000
12 months or longer, Unrealized losses	(861,000)		(861,000)		(518,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	280,215,000		280,215,000		210,558,000
Total Unrealized Losses	$ 9,585,000		$ 9,585,000		$ 2,460,000
Number of securities in Unrealized Loss Positions \| securities	32		32		26
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 9,585,000		$ 9,585,000		$ 2,460,000
Trust preferred securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Fair Value					2,548,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 months, Fair Value					0
Less than 12 months, Unrealized Losses					0
12 months or longer, Fair Value					2,548,000
12 months or longer, Unrealized losses					(345,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value					2,548,000
Total Unrealized Losses					$ 345,000
Number of securities in Unrealized Loss Positions \| securities					1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax					$ 345,000
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		0
After 1 through 5 years	2,015,000		2,015,000
After 5 through 10 years	0		0
After ten years	381,000		381,000
Fair Value	2,396,000		2,396,000		2,184,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0		$ 0		$ 0