Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 1,500
Due after one year through five years	4,199
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,699
Fair Value
Due in one year or less	1,515
Due after one year through five years	4,197
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,712
Investment securities available for sale, amortized cost	4,984,867	$ 5,368,259
Investment securities available for sale, at fair value	$ 4,967,414	5,396,812
Ratio of Fair Value to Amortized Cost	99.60%
Amortized Cost
Due in one year or less	$ 42,841
Due after one year through five years	244,257
Due after five years through ten years	253,429
Due after ten years	503,240
Held-to-maturity Debt Securities, Amortized Cost Basis	1,043,767
Amortized Cost	1,168,230	404,455
Fair Value
Due in one year or less	26,761
Due after one year through five years	255,899
Due after five years through ten years	261,934
Due after ten years	515,637
Held-to-maturity Securities, Debt Securities	1,060,231
Total debt securities	$ 1,184,442	413,067
Ratio of Fair Value to Amortized Cost	101.40%
Private Label [Member]
Fair Value
Investment securities available for sale, amortized cost	$ 1,722	2,297
Investment securities available for sale, at fair value	1,709	2,294
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
GNMA Commercial Mortgage-Related Securities [Member]
Fair Value
Investment securities available for sale, amortized cost	1,982,477	1,097,913
Investment securities available for sale, at fair value	1,955,310	1,073,893
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
Equity Securities [Member]
Fair Value
Investment securities available for sale, amortized cost	18
Investment securities available for sale, at fair value	54
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
FNMA and FHLMC [Member] | Residential Related Securities [Member]
Fair Value
Investment securities available for sale, amortized cost	1,388,995	3,534,240
Investment securities available for sale, at fair value	1,414,626	3,563,457
Amortized Cost
Amortized Cost	41,469
Fair Value
Total debt securities	41,337
GNMA [Member] | Residential Related Securities [Member]
Fair Value
Investment securities available for sale, amortized cost	1,605,956	165,863
Investment securities available for sale, at fair value	1,590,003	$ 167,332
Amortized Cost
Amortized Cost	82,994
Fair Value
Total debt securities	$ 82,874