Securities - Gross Unrealized Losses and Fair Value by Investment Category (Details) $ in Thousands	Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Available for Sale:
Number of positions, Less than 12 Months \| security	39	168
Fair Value, Less than 12 Months	$ 208,700	$ 509,808
Unrealized Losses, Less than 12 Months	$ (1,503)	$ (5,163)
Number of positions, 12 Months or More \| security	25	171
Fair value, 12 Months or More	$ 42,747	$ 312,698
Unrealized Losses, 12 Months or More	$ (2,634)	$ (13,106)
Number of positions \| security	64	339
Fair Value	$ 251,447	$ 822,506
Unrealized Losses	$ (4,137)	$ (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	1	2
Fair value, 12 Months or More	$ 1,009	$ 1,480
Unrealized Losses, 12 Months or More	$ (4)	$ (38)
Number of positions \| security	1	2
Fair Value	$ 1,009	$ 1,480
Unrealized Losses	$ (4)	$ (38)
Obligations of states and political subdivisions
Available for Sale:
Number of positions, Less than 12 Months \| security	10	34
Fair Value, Less than 12 Months	$ 16,669	$ 22,159
Unrealized Losses, Less than 12 Months	$ (156)	$ (193)
Number of positions, 12 Months or More \| security	0	26
Fair value, 12 Months or More	$ 0	$ 16,775
Unrealized Losses, 12 Months or More	$ 0	$ (374)
Number of positions \| security	10	60
Fair Value	$ 16,669	$ 38,934
Unrealized Losses	$ (156)	$ (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	$ 9,862	$ 10,633
Unrealized Losses, 12 Months or More	$ (2,298)	$ (1,726)
Number of positions \| security	2	2
Fair Value	$ 9,862	$ 10,633
Unrealized Losses	$ (2,298)	$ (1,726)
Other debt securities
Available for Sale:
Number of positions, Less than 12 Months \| security	1	12
Fair Value, Less than 12 Months	$ 610	$ 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	$ 750	$ 5,621
Unrealized Losses, 12 Months or More	$ (2)	$ (223)
Number of positions \| security	2	15
Fair Value	$ 1,360	$ 24,632
Unrealized Losses	$ (3)	$ (311)
Government agency mortgage backed securities \| Residential mortgage backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	19	91
Fair Value, Less than 12 Months	$ 143,731	$ 354,731
Unrealized Losses, Less than 12 Months	$ (1,058)	$ (3,945)
Number of positions, 12 Months or More \| security	19	73
Fair value, 12 Months or More	$ 29,922	$ 125,757
Unrealized Losses, 12 Months or More	$ (328)	$ (5,181)
Number of positions \| security	38	164
Fair Value	$ 173,653	$ 480,488
Unrealized Losses	$ (1,386)	$ (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	2	4
Fair value, 12 Months or More	$ 1,204	$ 7,468
Unrealized Losses, 12 Months or More	$ (2)	$ (310)
Number of positions \| security	2	9
Fair Value	$ 1,204	$ 13,974
Unrealized Losses	$ (2)	$ (384)
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	8	24
Fair Value, Less than 12 Months	$ 42,687	$ 97,451
Unrealized Losses, Less than 12 Months	$ (268)	$ (840)
Number of positions, 12 Months or More \| security	0	60
Fair value, 12 Months or More	$ 0	$ 140,076
Unrealized Losses, 12 Months or More	$ 0	$ (5,142)
Number of positions \| security	8	84
Fair Value	$ 42,687	$ 237,527
Unrealized Losses	$ (268)	$ (5,982)
Government agency collateralized mortgage obligations \| Commercial mortgage-backed securities
Available for Sale:
Number of positions, Less than 12 Months \| security	1	2
Fair Value, Less than 12 Months	$ 5,003	$ 9,950
Unrealized Losses, Less than 12 Months	$ (20)	$ (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	1	3
Fair Value	$ 5,003	$ 14,838
Unrealized Losses	$ (20)	$ (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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