Investment Securities - Schedule Of Investments Within The Available For Sale Portfolio That Had Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Less than 12 months	$ 556,675	$ 655,820
12 months or longer	0	553,979
Total fair value	556,675	1,209,799
Unrealized Losses
Less than 12 months	(92)	(3,616)
12 months or longer	0	(7,288)
Total unrealized losses	(92)	(10,904)
U.S. treasuries
Schedule of Investments [Line Items]
Less than 12 months	499,895	0
12 months or longer	0	100
Total fair value	499,895	100
Unrealized Losses
Less than 12 months	(4)	0
12 months or longer	0	0
Total unrealized losses	(4)	0
Government agency issued MBS
Schedule of Investments [Line Items]
Less than 12 months	40,798	174,983
12 months or longer	0	192,755
Total fair value	40,798	367,738
Unrealized Losses
Less than 12 months	(80)	(495)
12 months or longer	0	(2,061)
Total unrealized losses	(80)	(2,556)
Government agency issued CMO
Schedule of Investments [Line Items]
Less than 12 months	15,982	378,815
12 months or longer	0	361,124
Total fair value	15,982	739,939
Unrealized Losses
Less than 12 months	(8)	(1,970)
12 months or longer	0	(5,227)
Total unrealized losses	$ (8)	(7,197)
Other U.S. government agencies
Schedule of Investments [Line Items]
Less than 12 months		98,471
12 months or longer		0
Total fair value		98,471
Unrealized Losses
Less than 12 months		(1,121)
12 months or longer		0
Total unrealized losses		(1,121)
States and municipalities
Schedule of Investments [Line Items]
Less than 12 months		3,551
12 months or longer		0
Total fair value		3,551
Unrealized Losses
Less than 12 months		(30)
12 months or longer		0
Total unrealized losses		$ (30)