Investment Securities - Schedule Of Investments Within The Available For Sale Portfolio That Had Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Less than 12 months	$ 89,800	$ 655,820
12 months or longer	0	553,979
Total fair value	89,800	1,209,799
Unrealized Losses
Less than 12 months	(1,249)	(3,616)
12 months or longer	0	(7,288)
Total unrealized losses	(1,249)	(10,904)
Government agency issued MBS
Schedule of Investments [Line Items]
Less than 12 months		174,983
12 months or longer		192,755
Total fair value		367,738
Unrealized Losses
Less than 12 months		(495)
12 months or longer		(2,061)
Total unrealized losses		(2,556)
Government agency issued CMO
Schedule of Investments [Line Items]
Less than 12 months		378,815
12 months or longer		361,124
Total fair value		739,939
Unrealized Losses
Less than 12 months		(1,970)
12 months or longer		(5,227)
Total unrealized losses		(7,197)
Other U.S. government agencies
Schedule of Investments [Line Items]
Less than 12 months	88,334	98,471
12 months or longer	0	0
Total fair value	88,334	98,471
Unrealized Losses
Less than 12 months	(1,224)	(1,121)
12 months or longer	0	0
Total unrealized losses	(1,224)	(1,121)
States and municipalities
Schedule of Investments [Line Items]
Less than 12 months	1,466	3,551
12 months or longer	0	0
Total fair value	1,466	3,551
Unrealized Losses
Less than 12 months	(25)	(30)
12 months or longer	0	0
Total unrealized losses	$ (25)	$ (30)