Investments (Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Investment securities available for sale:
Fair Value, Less than 12 months	$ 2,802,433	$ 760,153
Unrealized Losses, Less than 12 months	25,541	6,466
Fair Value, 12 months or more	140,913	351,841
Unrealized Losses, Greater than 12 months	943	2,445
Fair Value, Total	2,943,346	1,111,994
Gross unrealized losses	26,484	8,911
Agency Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	301,934	268,622
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,040	3,197
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	124,577	328,777
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	707	2,376
Fair Value, Total	426,511	597,399
Gross unrealized losses	3,747	5,573
Residential Mortgage Backed Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,849,194	433,816
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14,305	1,241
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,068	23,064
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	19	69
Fair Value, Total	1,851,262	456,880
Gross unrealized losses	14,324	1,310
Commercial Mortgage Backed Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	648,803
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8,196
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
Fair Value, Total	648,803
Gross unrealized losses	8,196	0
Corporate bonds
Investment securities available for sale:
Fair Value, Total		57,715
Gross unrealized losses		2,028
Corporate Bonds
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,502	57,715
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	2,028
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	14,268	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	217	$ 0
Fair Value, Total	16,770
Gross unrealized losses	$ 217

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