Investments (Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investment securities available for sale:
Fair Value, Less than 12 months	$ 985,269	$ 2,778,014
Unrealized Losses, Less than 12 months	8,250	16,025
Fair Value, 12 months or more	246,943	332,953
Unrealized Losses, Greater than 12 months	3,233	1,794
Fair Value, Total	1,232,212	3,110,967
Unrealized Losses, Total	11,483	17,819
Investment securities held to maturity
Unrealized Losses, Total	22
Agency Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	436,066	347,081
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,542	1,827
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	60,920	63,947
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	374	414
Fair Value, Total	496,986	411,028
Unrealized Losses, Total	2,916	2,241
Residential Mortgage Backed Securities
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	366,901	2,387,293
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	625	14,016
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	177,167	264,257
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,166	1,371
Fair Value, Total	544,068	2,651,550
Unrealized Losses, Total	2,791	15,387
Investment securities held to maturity
Fair Value, Less than 12 months	70,108
Unrealized Losses, Less than 12 months	22
Fair Value, 12 months or more	0
Unrealized Losses, 12 months or more	0
Fair Value, Total	70,108
Unrealized Losses, Total	22
Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	75,480	35,926
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	603	59
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Fair Value, Total	75,480	35,926
Unrealized Losses, Total	603	59
Residential mortgage-backed securities
Investment securities held to maturity
Unrealized Losses, Total	22	0
Corporate bonds
Investment securities available for sale:
Fair Value, Total		12,463
Unrealized Losses, Total		132
Corporate Bonds
Investment securities available for sale:
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	106,822	7,714
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,480	123
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	8,856	4,749
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	693	9
Fair Value, Total	115,678
Unrealized Losses, Total	5,173
Other
Investment securities held to maturity
Unrealized Losses, Total	$ 0	$ 0

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