Securities - Schedule of Available-for-sale Securities with Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale securities
Fair Value, Less than 12 Months	$ 1,123,328	$ 417,782
Unrealized Losses, Less than 12 Months	16,600	3,014
Fair Value, 12 Months or Longer	315,534	9,266
Unrealized Losses, 12 Months or Longer	6,992	460
Fair Value	1,438,862	427,048
Unrealized Losses	23,592	3,474
U.S. Treasuries
Available-for-sale securities
Fair Value, Less than 12 Months	137,935
Unrealized Losses, Less than 12 Months	1,447
Fair Value, 12 Months or Longer	0
Unrealized Losses, 12 Months or Longer	0
Fair Value	137,935
Unrealized Losses	1,447
Obligations of U.S. Government sponsored entities
Available-for-sale securities
Fair Value, Less than 12 Months	326,852	310,711
Unrealized Losses, Less than 12 Months	3,879	1,992
Fair Value, 12 Months or Longer	276,710	0
Unrealized Losses, 12 Months or Longer	5,612	0
Fair Value	603,562	310,711
Unrealized Losses	9,491	1,992
Obligations of U.S. states and political subdivisions
Available-for-sale securities
Fair Value, Less than 12 Months	14,192	8,868
Unrealized Losses, Less than 12 Months	126	40
Fair Value, 12 Months or Longer	1,281	0
Unrealized Losses, 12 Months or Longer	19	0
Fair Value	15,473	8,868
Unrealized Losses	145	40
U.S. Government agencies
Available-for-sale securities
Fair Value, Less than 12 Months	34,808	10,560
Unrealized Losses, Less than 12 Months	405	396
Fair Value, 12 Months or Longer	1,285	1,819
Unrealized Losses, 12 Months or Longer	17	250
Fair Value	36,093	12,379
Unrealized Losses	422	646
U.S. Government sponsored entities
Available-for-sale securities
Fair Value, Less than 12 Months	609,541	87,643
Unrealized Losses, Less than 12 Months	10,743	586
Fair Value, 12 Months or Longer	33,837	5,068
Unrealized Losses, 12 Months or Longer	1,265	89
Fair Value	643,378	92,711
Unrealized Losses	12,008	675
U.S. corporate debt securities
Available-for-sale securities
Fair Value, Less than 12 Months	0	0
Unrealized Losses, Less than 12 Months	0	0
Fair Value, 12 Months or Longer	2,421	2,379
Unrealized Losses, 12 Months or Longer	79	121
Fair Value	2,421	2,379
Unrealized Losses	$ 79	$ 121

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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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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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