Securities - Gross Unrealized Losses and Fair Value by Investment Category (Details) $ in Thousands	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Available for Sale:
Number of positions, Less than 12 Months \| security	5	168
Fair Value, Less than 12 Months	$ 9,877	$ 509,808
Unrealized Losses, Less than 12 Months	$ (22)	$ (5,163)
Number of positions, 12 Months or More \| security	110	171
Fair value, 12 Months or More	$ 227,770	$ 312,698
Unrealized Losses, 12 Months or More	$ (4,419)	$ (13,106)
Number of positions \| security	115	339
Fair value	$ 237,647	$ 822,506
Unrealized Losses	$ (4,441)	$ (18,269)
Obligations of other U.S. Government agencies and corporations
Available for Sale:
Number of positions, Less than 12 Months \| security	0	0
Fair Value, Less than 12 Months	$ 0	$ 0
Unrealized Losses, Less than 12 Months	$ 0	$ 0
Number of positions, 12 Months or More \| security	2	2
Fair value, 12 Months or More	$ 1,507	$ 1,480
Unrealized Losses, 12 Months or More	$ (8)	$ (38)
Number of positions \| security	2	2
Fair value	$ 1,507	$ 1,480
Unrealized Losses	$ (8)	$ (38)
Obligations of states and political subdivisions
Available for Sale:
Number of positions, Less than 12 Months \| security	2	34
Fair Value, Less than 12 Months	$ 2,263	$ 22,159
Unrealized Losses, Less than 12 Months	$ (14)	$ (193)
Number of positions, 12 Months or More \| security	3	26
Fair value, 12 Months or More	$ 889	$ 16,775
Unrealized Losses, 12 Months or More	$ (3)	$ (374)
Number of positions \| security	5	60
Fair value	$ 3,152	$ 38,934
Unrealized Losses	$ (17)	$ (567)
Trust preferred securities
Available for Sale:
Number of positions, Less than 12 Months \| security	0	0
Fair Value, Less than 12 Months	$ 0	$ 0
Unrealized Losses, Less than 12 Months	$ 0	$ 0
Number of positions, 12 Months or More \| security	2	2
Fair value, 12 Months or More	$ 10,386	$ 10,633
Unrealized Losses, 12 Months or More	$ (1,859)	$ (1,726)
Number of positions \| security	2	2
Fair value	$ 10,386	$ 10,633
Unrealized Losses	$ (1,859)	$ (1,726)
Other debt securities
Available for Sale:
Number of positions, Less than 12 Months \| security	1	12
Fair Value, Less than 12 Months	$ 760	$ 19,011
Unrealized Losses, Less than 12 Months	$ (1)	$ (88)
Number of positions, 12 Months or More \| security	1	3
Fair value, 12 Months or More	$ 1,016	$ 5,621
Unrealized Losses, 12 Months or More	$ (10)	$ (223)
Number of positions \| security	2	15
Fair value	$ 1,776	$ 24,632
Unrealized Losses	$ (11)	$ (311)
Government agency mortgage backed securities \| Residential mortgage backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	1	91
Fair Value, Less than 12 Months	$ 762	$ 354,731
Unrealized Losses, Less than 12 Months	$ (1)	$ (3,945)
Number of positions, 12 Months or More \| security	65	73
Fair value, 12 Months or More	$ 123,783	$ 125,757
Unrealized Losses, 12 Months or More	$ (1,497)	$ (5,181)
Number of positions \| security	66	164
Fair value	$ 124,545	$ 480,488
Unrealized Losses	$ (1,498)	$ (9,126)
Government agency mortgage backed securities \| Commercial mortgage-backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	0	5
Fair Value, Less than 12 Months	$ 0	$ 6,506
Unrealized Losses, Less than 12 Months	$ 0	$ (74)
Number of positions, 12 Months or More \| security	3	4
Fair value, 12 Months or More	$ 6,004	$ 7,468
Unrealized Losses, 12 Months or More	$ (62)	$ (310)
Number of positions \| security	3	9
Fair value	$ 6,004	$ 13,974
Unrealized Losses	$ (62)	$ (384)
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	1	24
Fair Value, Less than 12 Months	$ 6,092	$ 97,451
Unrealized Losses, Less than 12 Months	$ (6)	$ (840)
Number of positions, 12 Months or More \| security	34	60
Fair value, 12 Months or More	$ 84,185	$ 140,076
Unrealized Losses, 12 Months or More	$ (980)	$ (5,142)
Number of positions \| security	35	84
Fair value	$ 90,277	$ 237,527
Unrealized Losses	$ (986)	$ (5,982)
Government agency collateralized mortgage obligations \| Commercial mortgage-backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	0	2
Fair Value, Less than 12 Months	$ 0	$ 9,950
Unrealized Losses, Less than 12 Months	$ 0	$ (23)
Number of positions, 12 Months or More \| security	0	1
Fair value, 12 Months or More	$ 0	$ 4,888
Unrealized Losses, 12 Months or More	$ 0	$ (112)
Number of positions \| security	0	3
Fair value	$ 0	$ 14,838
Unrealized Losses	$ 0	$ (135)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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