Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 4,500
Due after one year through five years	1,200
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,700
Fair Value
Due in one year or less	4,479
Due after one year through five years	1,200
Due after five years through ten years	0
Due after ten years	0
Total debt securities	5,679
Investment securities available for sale, amortized cost	4,724,895	$ 4,984,867
Investment securities available for sale, at fair value	$ 4,680,226	4,967,414
Ratio of Fair Value to Amortized Cost	99.10%
Amortized Cost
Due in one year or less	$ 38,791
Due after one year through five years	257,652
Due after five years through ten years	229,063
Due after ten years	620,337
Held-to-maturity Debt Securities, Amortized Cost Basis	1,145,843
Amortized Cost	1,273,536	1,168,230
Fair Value
Due in one year or less	28,517
Due after one year through five years	264,427
Due after five years through ten years	229,364
Due after ten years	615,367
Held-to-maturity Securities, Debt Securities	1,137,675
Total debt securities	$ 1,264,674	1,184,442
Ratio of Fair Value to Amortized Cost	99.30%
Private-label
Fair Value
Investment securities available for sale, amortized cost	$ 1,134	1,722
Investment securities available for sale, at fair value	1,121	1,709
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
GNMA commercial mortgage-related securities
Fair Value
Investment securities available for sale, amortized cost	2,064,508	1,982,477
Investment securities available for sale, at fair value	2,028,898	1,955,310
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
Equity securities
Fair Value
Investment securities available for sale, amortized cost	18
Investment securities available for sale, at fair value	123
Amortized Cost
Amortized Cost	0
Fair Value
Total debt securities	0
FNMA / FHLMC | Residential Related Securities
Fair Value
Investment securities available for sale, amortized cost	625,234	1,388,995
Investment securities available for sale, at fair value	639,930	1,414,626
Amortized Cost
Amortized Cost	37,697	41,469
Fair Value
Total debt securities	37,443	41,337
GNMA | Residential Related Securities
Fair Value
Investment securities available for sale, amortized cost	2,028,301	1,605,956
Investment securities available for sale, at fair value	2,004,475	1,590,003
Amortized Cost
Amortized Cost	89,996	82,994
Fair Value
Total debt securities	$ 89,556	$ 82,874