Investment Securities, AFS and HTM Securities Gross Unrealized Losses (Details) $ in Thousands	Dec. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (5,262)	$ (15,099)
Unrealized losses on available for sale securities, 12 months or more	(93,347)	(52,868)
Total unrealized losses on available for sale securities	(98,610)	(67,967)
Fair value of unrealized losses on available for sale securities, less than 12 months	613,612	1,593,503
Fair value of unrealized losses on available for sale securities, 12 months or more	3,009,417	1,906,992
Total fair value of unrealized losses on available for sale securities	$ 3,623,028	$ 3,500,495
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	41	92
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	190	105
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (4,053)	$ (4,491)
Held-to-maturity, Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions, less than 12 Months | security	298	202
Unrealized losses on held to maturity securities, 12 months or more	$ (43,780)	$ (21,331)
Total unrealized losses on held to maturity securities	(47,835)	(25,822)
Fair value of unrealized losses on held to maturity securities, less than 12 months	$ 390,929	$ 457,289
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, 12 Months or Longer | security	865	183
Fair value of unrealized losses on held to maturity securities, 12 months or more	$ 1,349,063	$ 751,088
Total fair value of unrealized losses on held to maturity securities	1,739,992	1,208,377
U.S. Treasury securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	0	(7)
Unrealized losses on available for sale securities, 12 months or more	(1)	0
Total unrealized losses on available for sale securities	(1)	(7)
Fair value of unrealized losses on available for sale securities, less than 12 months	0	996
Fair value of unrealized losses on available for sale securities, 12 months or more	999	0
Total fair value of unrealized losses on available for sale securities	$ 999	$ 996
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	0	1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	1	0
Obligations of state and political subdivisions (municipal securities)
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (2,860)	$ (746)
Unrealized losses on held to maturity securities, 12 months or more	(12,419)	(2,431)
Total unrealized losses on held to maturity securities	(15,279)	(3,177)
Fair value of unrealized losses on held to maturity securities, less than 12 months	313,212	122,761
Fair value of unrealized losses on held to maturity securities, 12 months or more	509,374	127,043
Total fair value of unrealized losses on held to maturity securities	$ 822,586	$ 249,804
Obligations of state and political subdivisions (municipal securities) | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	272	157
Obligations of state and political subdivisions (municipal securities) | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	752	132
Private-label
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (4)	$ 0
Unrealized losses on available for sale securities, 12 months or more	0	(8)
Total unrealized losses on available for sale securities	(4)	(8)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,003	0
Fair value of unrealized losses on available for sale securities, 12 months or more	0	1,059
Total fair value of unrealized losses on available for sale securities	$ 1,003	$ 1,059
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	1	0
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0	1
GNMA commercial mortgage-related securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ 0	$ (5,554)
Unrealized losses on available for sale securities, 12 months or more	(52,512)	(28,347)
Total unrealized losses on available for sale securities	(52,512)	(33,901)
Fair value of unrealized losses on available for sale securities, less than 12 months	0	480,514
Fair value of unrealized losses on available for sale securities, 12 months or more	1,220,854	1,026,642
Total fair value of unrealized losses on available for sale securities	$ 1,220,854	$ 1,507,156
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	0	33
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	93	70
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ 0	$ (299)
Unrealized losses on held to maturity securities, 12 months or more	(22,579)	(15,457)
Total unrealized losses on held to maturity securities	(22,579)	(15,756)
Fair value of unrealized losses on held to maturity securities, less than 12 months	0	52,997
Fair value of unrealized losses on held to maturity securities, 12 months or more	490,414	486,891
Total fair value of unrealized losses on held to maturity securities	$ 490,414	$ 539,888
GNMA commercial mortgage-related securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	0	2
GNMA commercial mortgage-related securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	25	23
FFELP asset backed securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (698)	$ (13)
Unrealized losses on available for sale securities, 12 months or more	0	0
Total unrealized losses on available for sale securities	(698)	(13)
Fair value of unrealized losses on available for sale securities, less than 12 months	142,432	12,158
Fair value of unrealized losses on available for sale securities, 12 months or more	0	0
Total fair value of unrealized losses on available for sale securities	$ 142,432	$ 12,158
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	13	1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0	0
Debt Securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months		$ (12)
Unrealized losses on available for sale securities, 12 months or more		0
Total unrealized losses on available for sale securities		(12)
Fair value of unrealized losses on available for sale securities, less than 12 months		188
Fair value of unrealized losses on available for sale securities, 12 months or more		0
Total fair value of unrealized losses on available for sale securities		$ 188
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security		1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security		0
Equity securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months		$ (14)
Unrealized losses on available for sale securities, 12 months or more		0
Total unrealized losses on available for sale securities		(14)
Fair value of unrealized losses on available for sale securities, less than 12 months		1,487
Fair value of unrealized losses on available for sale securities, 12 months or more		0
Total fair value of unrealized losses on available for sale securities		$ 1,487
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security		3
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security		0
FNMA / FHLMC | Residential Related Securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (31)	$ (572)
Unrealized losses on available for sale securities, 12 months or more	(3,479)	(2,062)
Total unrealized losses on available for sale securities	(3,510)	(2,634)
Fair value of unrealized losses on available for sale securities, less than 12 months	17,993	69,939
Fair value of unrealized losses on available for sale securities, 12 months or more	189,405	142,093
Total fair value of unrealized losses on available for sale securities	$ 207,398	$ 212,032
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	15	9
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	17	9
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (780)	$ (73)
Unrealized losses on held to maturity securities, 12 months or more	(1,015)	(417)
Total unrealized losses on held to maturity securities	(1,795)	(490)
Fair value of unrealized losses on held to maturity securities, less than 12 months	57,896	13,143
Fair value of unrealized losses on held to maturity securities, 12 months or more	28,888	16,262
Total fair value of unrealized losses on held to maturity securities	$ 86,784	$ 29,405
FNMA / FHLMC | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	13	8
FNMA / FHLMC | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	22	10
GNMA | Residential Related Securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (4,529)	$ (8,927)
Unrealized losses on available for sale securities, 12 months or more	(37,355)	(22,451)
Total unrealized losses on available for sale securities	(41,885)	(31,378)
Fair value of unrealized losses on available for sale securities, less than 12 months	452,183	1,028,221
Fair value of unrealized losses on available for sale securities, 12 months or more	1,598,159	737,198
Total fair value of unrealized losses on available for sale securities	$ 2,050,342	$ 1,765,419
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	12	44
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	79	25
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (414)	$ (3,373)
Unrealized losses on held to maturity securities, 12 months or more	(7,767)	(3,026)
Total unrealized losses on held to maturity securities	(8,181)	(6,399)
Fair value of unrealized losses on held to maturity securities, less than 12 months	19,822	268,388
Fair value of unrealized losses on held to maturity securities, 12 months or more	320,387	120,892
Total fair value of unrealized losses on held to maturity securities	$ 340,209	$ 389,280
GNMA | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Less Than One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	13	35
GNMA | Residential Related Securities | Held To Maturity Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions Greater Than Or Equal To One Year [Member]
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Number of held to maturity securities in a continuous unrealized loss position | security	66	18