Investment Securities - Unrealized Losses and Fair Value of Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value
Less than Twelve Months	$ 19,271	$ 101,621
More than Twelve Months, Fair Value	992,382	1,086,150
Total	1,011,653	1,187,771
Unrealized Losses
Less than Twelve Months	(158)	(1,207)
More than Twelve Months	(29,446)	(46,532)
Total	(29,604)	(47,739)
U.S. government agency securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months, Fair Value	5,707	6,074
Total	5,707	6,074
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(183)	(135)
Total	(183)	(135)
Obligations of states and state agencies
Fair Value
Less than Twelve Months	0	16,098
More than Twelve Months, Fair Value	100,897	138,437
Total	100,897	154,535
Unrealized Losses
Less than Twelve Months	0	(266)
More than Twelve Months	(2,086)	(5,469)
Total	(2,086)	(5,735)
Municipal bonds
Fair Value
Less than Twelve Months	1,188	3,335
More than Twelve Months, Fair Value	15,236	60,078
Total	16,424	63,413
Unrealized Losses
Less than Twelve Months	(20)	(37)
More than Twelve Months	(113)	(1,324)
Total	(133)	(1,361)
Obligations of states and political subdivisions
Fair Value
Less than Twelve Months	1,188	19,433
More than Twelve Months, Fair Value	116,133	198,515
Total	117,321	217,948
Unrealized Losses
Less than Twelve Months	(20)	(303)
More than Twelve Months	(2,199)	(6,793)
Total	(2,219)	(7,096)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	13,136	72,240
More than Twelve Months, Fair Value	835,504	846,671
Total	848,640	918,911
Unrealized Losses
Less than Twelve Months	(85)	(852)
More than Twelve Months	(21,146)	(33,516)
Total	(21,231)	(34,368)
Trust preferred securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months, Fair Value	30,180	30,055
Total	30,180	30,055
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(5,776)	(5,923)
Total	(5,776)	(5,923)
Corporate and other debt securities
Fair Value
Less than Twelve Months	4,947	9,948
More than Twelve Months, Fair Value	4,858	4,835
Total	9,805	14,783
Unrealized Losses
Less than Twelve Months	(53)	(52)
More than Twelve Months	(142)	(165)
Total	$ (195)	$ (217)

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months.

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