Investment Securities - Schedule Of Investments Within The Available For Sale Portfolio That Had Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Less than 12 months	$ 4,221	$ 960,053
12 months or longer	1,244,506	3,112,632
Total fair value	1,248,727	4,072,685
Unrealized Losses
Less than 12 months	(26)	(15,826)
12 months or longer	(13,549)	(92,005)
Total unrealized losses	(13,575)	(107,831)
U.S. treasuries
Schedule of Investments [Line Items]
Less than 12 months	0	0
12 months or longer	100	98
Total fair value	100	98
Unrealized Losses
Less than 12 months	0	0
12 months or longer	0	(2)
Total unrealized losses	0	(2)
Government agency issued MBS
Schedule of Investments [Line Items]
Less than 12 months	2,284	597,008
12 months or longer	515,618	1,537,106
Total fair value	517,902	2,134,114
Unrealized Losses
Less than 12 months	(24)	(12,335)
12 months or longer	(5,025)	(46,065)
Total unrealized losses	(5,049)	(58,400)
Government agency issued CMO
Schedule of Investments [Line Items]
Less than 12 months	0	290,863
12 months or longer	703,604	1,560,420
Total fair value	703,604	1,851,283
Unrealized Losses
Less than 12 months	0	(2,860)
12 months or longer	(8,388)	(45,821)
Total unrealized losses	(8,388)	(48,681)
Other U.S. government agencies
Schedule of Investments [Line Items]
Less than 12 months		29,776
12 months or longer		0
Total fair value		29,776
Unrealized Losses
Less than 12 months		(73)
12 months or longer		0
Total unrealized losses		(73)
Corporates and other debt
Schedule of Investments [Line Items]
Less than 12 months	0	25,114
12 months or longer	25,184	15,008
Total fair value	25,184	40,122
Unrealized Losses
Less than 12 months	0	(344)
12 months or longer	(136)	(117)
Total unrealized losses	(136)	(461)
States and municipalities
Schedule of Investments [Line Items]
Less than 12 months	1,937	17,292
12 months or longer	0	0
Total fair value	1,937	17,292
Unrealized Losses
Less than 12 months	(2)	(214)
12 months or longer	0	0
Total unrealized losses	$ (2)	$ (214)