Investment Securities, AFS and HTM Securities Gross Unrealized Losses (Details) $ in Thousands	Jun. 30, 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	$ (41,975)	$ (15,099)
Unrealized losses on available for sale securities, 12 months or more	(81,093)	(52,868)
Total unrealized losses on available for sale securities	(123,068)	(67,967)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,939,830	1,593,503
Fair value of unrealized losses on available for sale securities, 12 months or more	1,950,298	1,906,992
Total fair value of unrealized losses on available for sale securities	$ 3,890,128	$ 3,500,495
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	110	92
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	120	105
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (20,207)	$ (4,491)
Unrealized losses on held to maturity securities, 12 months or more	(36,648)	(21,331)
Total unrealized losses on held to maturity securities	$ (56,856)	$ (25,822)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, 12 Months or Longer | security	196	183
Fair value of unrealized losses on held to maturity securities, less than 12 months	$ 950,678	$ 457,289
Fair value of unrealized losses on held to maturity securities, 12 months or more	758,635	751,088
Total fair value of unrealized losses on held to maturity securities	$ 1,709,313	$ 1,208,377
Held-to-maturity, Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Positions, less than 12 Months | security	977	202
US 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
Unrealized losses on available for sale securities, 12 months or more	(6)
Total unrealized losses on available for sale securities	(6)
Fair value of unrealized losses on available for sale securities, less than 12 months	0
Fair value of unrealized losses on available for sale securities, 12 months or more	996
Total fair value of unrealized losses on available for sale securities	$ 996
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	0
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	1
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	$ (10,814)	$ (746)
Unrealized losses on held to maturity securities, 12 months or more	(6,884)	(2,431)
Total unrealized losses on held to maturity securities	(17,698)	(3,177)
Fair value of unrealized losses on held to maturity securities, less than 12 months	609,381	122,761
Fair value of unrealized losses on held to maturity securities, 12 months or more	128,244	127,043
Total fair value of unrealized losses on held to maturity securities	$ 737,625	$ 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	890	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	142	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	$ 0	$ 0
Unrealized losses on available for sale securities, 12 months or more	(5)	(8)
Total unrealized losses on available for sale securities	(5)	(8)
Fair value of unrealized losses on available for sale securities, less than 12 months	0	0
Fair value of unrealized losses on available for sale securities, 12 months or more	1,031	1,059
Total fair value of unrealized losses on available for sale securities	$ 1,031	$ 1,059
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	0	0
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	1	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	$ (8,821)	$ (5,554)
Unrealized losses on available for sale securities, 12 months or more	(43,577)	(28,347)
Total unrealized losses on available for sale securities	(52,398)	(33,901)
Fair value of unrealized losses on available for sale securities, less than 12 months	284,733	480,514
Fair value of unrealized losses on available for sale securities, 12 months or more	1,063,701	1,026,642
Total fair value of unrealized losses on available for sale securities	$ 1,348,434	$ 1,507,156
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	22	33
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	80	70
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (813)
Unrealized losses on held to maturity securities, 12 months or more	(23,019)
Total unrealized losses on held to maturity securities	(23,832)
Fair value of unrealized losses on held to maturity securities, less than 12 months	29,243
Fair value of unrealized losses on held to maturity securities, 12 months or more	478,570
Total fair value of unrealized losses on held to maturity securities	$ 507,813
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	1
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	24
Federal Family Education Loan Program (FFELP) Guaranteed Loans [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	$ (111)	$ (13)
Unrealized losses on available for sale securities, 12 months or more	0	0
Total unrealized losses on available for sale securities	(111)	(13)
Fair value of unrealized losses on available for sale securities, less than 12 months	100,757	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	$ 100,757	$ 12,158
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	7	1
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	0	0
Other Debt And Other 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		$ (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 [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		$ (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 and FHLMC | US 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		$ (7)
Unrealized losses on available for sale securities, 12 months or more		0
Total unrealized losses on available for sale securities		(7)
Fair value of unrealized losses on available for sale securities, less than 12 months		996
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		$ 996
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
FNMA and 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	$ (1,613)	$ (572)
Unrealized losses on available for sale securities, 12 months or more	(3,620)	(2,062)
Total unrealized losses on available for sale securities	(5,233)	(2,634)
Fair value of unrealized losses on available for sale securities, less than 12 months	100,946	69,939
Fair value of unrealized losses on available for sale securities, 12 months or more	128,509	142,093
Total fair value of unrealized losses on available for sale securities	$ 229,455	$ 212,032
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	19	9
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	9	9
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (1,518)	$ (73)
Unrealized losses on held to maturity securities, 12 months or more	(788)	(417)
Total unrealized losses on held to maturity securities	(2,306)	(490)
Fair value of unrealized losses on held to maturity securities, less than 12 months	76,046	13,143
Fair value of unrealized losses on held to maturity securities, 12 months or more	14,728	16,262
Total fair value of unrealized losses on held to maturity securities	$ 90,774	$ 29,405
FNMA and 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	25	8
FNMA and 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	10	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	$ (31,430)	$ (8,927)
Unrealized losses on available for sale securities, 12 months or more	(33,885)	(22,451)
Total unrealized losses on available for sale securities	(65,315)	(31,378)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,453,394	1,028,221
Fair value of unrealized losses on available for sale securities, 12 months or more	756,061	737,198
Total fair value of unrealized losses on available for sale securities	$ 2,209,455	$ 1,765,419
Number of available for sale securities in a continuous unrealized loss position less than twelve months | security	62	44
Number of available for sale securities in a continuous unrealized loss position for twelve months or more | security	29	25
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months	$ (7,062)	$ (3,373)
Unrealized losses on held to maturity securities, 12 months or more	(5,957)	(3,026)
Total unrealized losses on held to maturity securities	(13,019)	(6,399)
Fair value of unrealized losses on held to maturity securities, less than 12 months	236,008	268,388
Fair value of unrealized losses on held to maturity securities, 12 months or more	137,093	120,892
Total fair value of unrealized losses on held to maturity securities	$ 373,101	$ 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	61	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	20	18
GNMA | GNMA Commercial Mortgage-Related Securities
Held-to-maturity Securities Continuous Unrealized Loss Position [Abstract]
Unrealized losses on held to maturity securities, less than 12 months		$ (299)
Unrealized losses on held to maturity securities, 12 months or more		(15,457)
Total unrealized losses on held to maturity securities		(15,756)
Fair value of unrealized losses on held to maturity securities, less than 12 months		52,997
Fair value of unrealized losses on held to maturity securities, 12 months or more		486,891
Total fair value of unrealized losses on held to maturity securities		$ 539,888
GNMA | 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		2
GNMA | 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		23