Securities Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	77	203
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 925,471	$ 2,182,644
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	419,576	897,351
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,345,047	3,079,995
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,227	10,928
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	699	9,358
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 4,926	$ 20,286
Municipal and other tax-exempt securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	11
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 19,768
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	19,768
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	97
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 97
Residential agency mortgage-backed securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	32	133
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 630,460	$ 1,352,597
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	165,726	686,002
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	796,186	2,038,599
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,178	6,690
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	221	8,423
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 3,399	$ 15,113
Commercial agency mortgage-backed securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	29	69
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 264,836	$ 830,047
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	253,378	210,877
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	518,214	1,040,924
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	923	4,238
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	450	907
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 1,373	$ 5,145
Other debt securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	5	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 10,407	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	472	472
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	10,879	472
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	29	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	28	28
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 57	$ 28