Securities - Investment Category and Length of Time in Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	79	168
Fair Value, Less than 12 Months	$ 331,023	$ 509,808
Unrealized Losses, Less than 12 Months	$ (2,394)	$ (5,163)
Number of positions, 12 Months or More \| security	22	171
Fair Value, 12 Months or More	$ 33,700	$ 312,698
Unrealized Losses, 12 Months or More	$ (2,484)	$ (13,106)
Number of positions \| security	101	339
Fair Value	$ 364,723	$ 822,506
Unrealized Losses	$ (4,878)	$ (18,269)
Obligations of other U.S. Government agencies and corporations
Unrealized losses and fair value by investment category
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	$ 1,008	$ 1,480
Unrealized Losses, 12 Months or More	$ (3)	$ (38)
Number of positions \| security	1	2
Fair Value	$ 1,008	$ 1,480
Unrealized Losses	$ (3)	$ (38)
Obligations of states and political subdivisions
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	26	34
Fair Value, Less than 12 Months	$ 33,902	$ 22,159
Unrealized Losses, Less than 12 Months	$ (365)	$ (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	26	60
Fair Value	$ 33,902	$ 38,934
Unrealized Losses	$ (365)	$ (567)
Trust preferred securities
Unrealized losses and fair value by investment category
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	$ 9,986	$ 10,633
Unrealized Losses, 12 Months or More	$ (2,167)	$ (1,726)
Number of positions \| security	2	2
Fair Value	$ 9,986	$ 10,633
Unrealized Losses	$ (2,167)	$ (1,726)
Other debt securities
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	3	12
Fair Value, Less than 12 Months	$ 8,737	$ 19,011
Unrealized Losses, Less than 12 Months	$ (131)	$ (88)
Number of positions, 12 Months or More \| security	1	3
Fair Value, 12 Months or More	$ 741	$ 5,621
Unrealized Losses, 12 Months or More	$ (1)	$ (223)
Number of positions \| security	4	15
Fair Value	$ 9,478	$ 24,632
Unrealized Losses	$ (132)	$ (311)
Government agency mortgage backed securities \| Residential mortgage backed securities
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	37	91
Fair Value, Less than 12 Months	$ 233,179	$ 354,731
Unrealized Losses, Less than 12 Months	$ (1,504)	$ (3,945)
Number of positions, 12 Months or More \| security	16	73
Fair Value, 12 Months or More	$ 20,775	$ 125,757
Unrealized Losses, 12 Months or More	$ (312)	$ (5,181)
Number of positions \| security	53	164
Fair Value	$ 253,954	$ 480,488
Unrealized Losses	$ (1,816)	$ (9,126)
Government agency mortgage backed securities \| Commercial mortgage backed securities
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	1	5
Fair Value, Less than 12 Months	$ 4,976	$ 6,506
Unrealized Losses, Less than 12 Months	$ (23)	$ (74)
Number of positions, 12 Months or More \| security	2	4
Fair Value, 12 Months or More	$ 1,190	$ 7,468
Unrealized Losses, 12 Months or More	$ (1)	$ (310)
Number of positions \| security	3	9
Fair Value	$ 6,166	$ 13,974
Unrealized Losses	$ (24)	$ (384)
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	11	24
Fair Value, Less than 12 Months	$ 45,319	$ 97,451
Unrealized Losses, Less than 12 Months	$ (262)	$ (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	11	84
Fair Value	$ 45,319	$ 237,527
Unrealized Losses	$ (262)	$ (5,982)
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities
Unrealized losses and fair value by investment category
Number of positions, Less than 12 Months \| security	1	2
Fair Value, Less than 12 Months	$ 4,910	$ 9,950
Unrealized Losses, Less than 12 Months	$ (109)	$ (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	$ 4,910	$ 14,838
Unrealized Losses	$ (109)	$ (135)

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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