Investment Securities - Unrealized Losses and Fair Value of Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value
Less than Twelve Months	$ 142,215	$ 101,621
More than Twelve Months, Fair Value	390,188	1,086,150
Total	532,403	1,187,771
Unrealized Losses
Less than Twelve Months	(281)	(1,207)
More than Twelve Months	(10,677)	(46,532)
Total	(10,958)	(47,739)
U.S. government agency securities
Fair Value
Less than Twelve Months	2,093	0
More than Twelve Months, Fair Value	0	6,074
Total	2,093	6,074
Unrealized Losses
Less than Twelve Months	(2)	0
More than Twelve Months	0	(135)
Total	(2)	(135)
Obligations of states and state agencies
Fair Value
Less than Twelve Months	11,459	16,098
More than Twelve Months, Fair Value	35,927	138,437
Total	47,386	154,535
Unrealized Losses
Less than Twelve Months	(45)	(266)
More than Twelve Months	(540)	(5,469)
Total	(585)	(5,735)
Municipal bonds
Fair Value
Less than Twelve Months	4,379	3,335
More than Twelve Months, Fair Value	784	60,078
Total	5,163	63,413
Unrealized Losses
Less than Twelve Months	(9)	(37)
More than Twelve Months	(16)	(1,324)
Total	(25)	(1,361)
Obligations of states and political subdivisions
Fair Value
Less than Twelve Months	15,838	19,433
More than Twelve Months, Fair Value	36,711	198,515
Total	52,549	217,948
Unrealized Losses
Less than Twelve Months	(54)	(303)
More than Twelve Months	(556)	(6,793)
Total	(610)	(7,096)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	117,588	72,240
More than Twelve Months, Fair Value	319,039	846,671
Total	436,627	918,911
Unrealized Losses
Less than Twelve Months	(171)	(852)
More than Twelve Months	(3,594)	(33,516)
Total	(3,765)	(34,368)
Trust preferred securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months, Fair Value	29,491	30,055
Total	29,491	30,055
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(6,475)	(5,923)
Total	(6,475)	(5,923)
Corporate and other debt securities
Fair Value
Less than Twelve Months	6,696	9,948
More than Twelve Months, Fair Value	4,947	4,835
Total	11,643	14,783
Unrealized Losses
Less than Twelve Months	(54)	(52)
More than Twelve Months	(52)	(165)
Total	$ (106)	$ (217)

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

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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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