Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost
Available for Sale, Due in one year or less	$ 2,500
Available for Sale, Due after one year through five years	3,200
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	5,700
Investment securities available for sale, amortized cost	4,865,970	$ 4,984,867
Fair Value
Available for Sale, Due in one year or less	2,530
Available for Sale, Due after one year through five years	3,200
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	5,730
Investment securities available for sale, at fair value	$ 4,905,841	4,967,414
Ratio of Fair Value to Amortized Cost	100.80%
Amortized Cost
Held to Maturity, Due in one year or less	$ 46,749
Held to Maturity, Due after one year through five years	243,423
Held to Maturity, Due after five years through ten years	245,683
Held to Maturity, Due after ten years	518,902
Held to Maturity, Debt Securities, Amortized Cost Basis	1,054,757
Held to Maturity Amortized Cost	1,176,821	1,168,230
Fair Value
Held to Maturity, Due in one year or less	32,151
Held to Maturity, Due after one year through five years	255,338
Held to Maturity, Due after five years through ten years	255,755
Held to Maturity, Due after ten years	537,339
Held to Maturity, Securities, Debt Securities	1,080,583
Held to Maturity, Total debt securities	$ 1,204,345	1,184,442
Ratio of Fair Value to Amortized Cost	102.30%
Private Label [Member]
Amortized Cost
Investment securities available for sale, amortized cost	$ 1,535	1,722
Fair Value
Investment securities available for sale, at fair value	1,512	1,709
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
GNMA Commercial Mortgage-Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	2,053,540	1,982,477
Fair Value
Investment securities available for sale, at fair value	2,047,865	1,955,310
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
Equity Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	18
Fair Value
Investment securities available for sale, at fair value	75
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
FNMA and FHLMC [Member] \| Residential Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	1,268,929	1,388,995
Fair Value
Investment securities available for sale, at fair value	1,303,404	1,414,626
Amortized Cost
Held to Maturity Amortized Cost	40,404	41,469
Fair Value
Held to Maturity, Total debt securities	41,021	41,337
GNMA [Member] \| Residential Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	1,536,248	1,605,956
Fair Value
Investment securities available for sale, at fair value	1,547,255	1,590,003
Amortized Cost
Held to Maturity Amortized Cost	81,660	82,994
Fair Value
Held to Maturity, Total debt securities	$ 82,741	$ 82,874

Held-to-maturity Debt Securities, Amortized Cost Basis

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