Securities - Gross Unrealized Losses and Fair Value by Investment Category (Details) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Available for Sale:
Number of positions, Less than 12 Months \| security	143	21
Fair Value, Less than 12 Months	$ 1,512,911	$ 75,359
Unrealized Losses, Less than 12 Months	$ (14,503)	$ (211)
Number of positions, 12 Months or More \| security	5	4
Fair value, 12 Months or More	$ 7,327	$ 10,037
Unrealized Losses, 12 Months or More	$ (123)	$ (3,004)
Number of positions \| security	148	25
Fair Value	$ 1,520,238	$ 85,396
Unrealized Losses	$ (14,626)	$ (3,215)
Obligations of states and political subdivisions
Available for Sale:
Number of positions, Less than 12 Months \| security	46	6
Fair Value, Less than 12 Months	$ 145,658	$ 9,403
Unrealized Losses, Less than 12 Months	$ (2,338)	$ (45)
Number of positions, 12 Months or More \| security	3	0
Fair value, 12 Months or More	$ 3,884	$ 0
Unrealized Losses, 12 Months or More	$ (88)	$ 0
Number of positions \| security	49	6
Fair Value	$ 149,542	$ 9,403
Unrealized Losses	$ (2,426)	$ (45)
Trust preferred securities
Available for Sale:
Number of positions, Less than 12 Months \| security		0
Fair Value, Less than 12 Months		$ 0
Unrealized Losses, Less than 12 Months		$ 0
Number of positions, 12 Months or More \| security		2
Fair value, 12 Months or More		$ 9,012
Unrealized Losses, 12 Months or More		$ (3,001)
Number of positions \| security		2
Fair Value		$ 9,012
Unrealized Losses		$ (3,001)
Other debt securities
Available for Sale:
Number of positions, Less than 12 Months \| security		4
Fair Value, Less than 12 Months		$ 3,330
Unrealized Losses, Less than 12 Months		$ (70)
Number of positions, 12 Months or More \| security		1
Fair value, 12 Months or More		$ 566
Unrealized Losses, 12 Months or More		$ (3)
Number of positions \| security		5
Fair Value		$ 3,896
Unrealized Losses		$ (73)
Government agency mortgage backed securities \| Residential mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months \| security	45	2
Fair Value, Less than 12 Months	$ 508,398	$ 19,755
Unrealized Losses, Less than 12 Months	$ (3,689)	$ (23)
Number of positions, 12 Months or More \| security	0	0
Fair value, 12 Months or More	$ 0	$ 0
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions \| security	45	2
Fair Value	$ 508,398	$ 19,755
Unrealized Losses	$ (3,689)	$ (23)
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months \| security	17	1
Fair Value, Less than 12 Months	$ 3,673	$ 1,538
Unrealized Losses, Less than 12 Months	$ (1)	$ (1)
Number of positions, 12 Months or More \| security	1	1
Fair value, 12 Months or More	$ 439	$ 459
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions \| security	18	2
Fair Value	$ 4,112	$ 1,997
Unrealized Losses	$ (1)	$ (1)
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months \| security	33	5
Fair Value, Less than 12 Months	$ 726,128	$ 27,143
Unrealized Losses, Less than 12 Months	$ (6,172)	$ (51)
Number of positions, 12 Months or More \| security	0	0
Fair value, 12 Months or More	$ 0	$ 0
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions \| security	33	5
Fair Value	$ 726,128	$ 27,143
Unrealized Losses	$ (6,172)	$ (51)
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months \| security	2	3
Fair Value, Less than 12 Months	$ 129,054	$ 14,190
Unrealized Losses, Less than 12 Months	$ (2,303)	$ (21)
Number of positions, 12 Months or More \| security	1	0
Fair value, 12 Months or More	$ 3,004	$ 0
Unrealized Losses, 12 Months or More	$ (35)	$ 0
Number of positions \| security	3	3
Fair Value	$ 132,058	$ 14,190
Unrealized Losses	$ (2,338)	$ (21)

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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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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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