Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 2,332,324	$ 880,507
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	24,252	6,453
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	229,333	18,597
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,985	815
Debt Securities, Available-for-sale, Unrealized Loss Position	2,561,657	899,104
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	30,237	7,268
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,744,928	575,329
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	15,723	3,728
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	69,031	18,527
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,292	815
Debt Securities, Available-for-sale, Unrealized Loss Position	1,813,959	593,856
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	18,015	4,543
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	170,492	143,764
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,490	2,076
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	89,936	70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,532	0
Debt Securities, Available-for-sale, Unrealized Loss Position	260,428	143,834
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,022	2,076
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	315,235	86,471
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,406	592
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	20,961	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	566	0
Debt Securities, Available-for-sale, Unrealized Loss Position	336,196	86,471
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	4,972	592
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	101,669	74,943
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	633	57
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	49,405	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	595	0
Debt Securities, Available-for-sale, Unrealized Loss Position	151,074	74,943
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 1,228	$ 57

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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