Investment Securities and Equity Securities with Readily Determinable Fair Values (Fair Value and Gross Unrealized Loss) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available for sale:
Fair value, less than 12 months	$ 7,906	$ 523,797
Unrealized losses, less than 12 Months	(188)	(2,274)
Fair value, 12 months or more	361	1,448,109
Unrealized losses, 12 Months or More	(3)	(14,340)
Fair value, Total	8,267	1,971,906
Unrealized losses, Total	(191)	(16,614)
Residential mortgage-backed securities
Available for sale:
Fair value, less than 12 months	7,144	523,031
Unrealized losses, less than 12 Months	(179)	(2,269)
Fair value, 12 months or more	361	1,448,109
Unrealized losses, 12 Months or More	(3)	(14,340)
Fair value, Total	7,505	1,971,140
Unrealized losses, Total	(182)	(16,609)
Obligations of states and political subdivisions
Available for sale:
Fair value, less than 12 months	762	766
Unrealized losses, less than 12 Months	(9)	(5)
Fair value, Total	762	766
Unrealized losses, Total	$ (9)	$ (5)