Investments (Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 3,241,180	$ 760,153
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	33,057	6,466
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	131,437	351,841
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	694	2,445
Debt Securities, Available-for-sale, Unrealized Loss Position	3,372,617	1,111,994
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	33,751	8,911
Agency Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	302,114	268,622
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,857	3,197
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	119,231	328,777
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	623	2,376
Debt Securities, Available-for-sale, Unrealized Loss Position	421,345	597,399
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3,480	5,573
Residential Mortgage Backed Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,137,675	433,816
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	17,752	1,241
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,762	23,064
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15	69
Debt Securities, Available-for-sale, Unrealized Loss Position	2,139,437	456,880
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	17,767	1,310
Commercial Mortgage Backed Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	758,798
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11,406
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	758,798
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	11,406
Corporate bonds
Investment securities available for sale:
Debt Securities, Available-for-sale, Unrealized Loss Position		57,715
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		2,028
Corporate Bonds
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	42,593	57,715
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,042	2,028
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	10,444	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	56	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position	53,037
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 1,098

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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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