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Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Amortized Cost |  |
Available for Sale, Due in one year or less | $ 3,001 |
Available for Sale, Due after one year through five years | 1,000 |
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 | 4,001 |
Investment securities available for sale, amortized cost | 4,377,443 | $ 4,100,417
Fair Value |  |
Available for Sale, Due in one year or less | 2,996 |
Available for Sale, Due after one year through five years | 1,000 |
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 | 3,996 |
Investment securities available for sale, at fair value | $ 4,261,651 | 4,043,446
Ratio of Fair Value to Amortized Cost | 97.40% |
Amortized Cost |  |
Held to Maturity, Due in one year or less | $ 46,938 |
Held to Maturity, Due after one year through five years | 200,725 |
Held to Maturity, Due after five years through ten years | 366,997 |
Held to Maturity, Due after ten years | 978,487 |
Held to Maturity, Debt Securities, Amortized Cost Basis | 1,593,147 |
Held to Maturity Amortized Cost | 2,602,247 | 2,282,853
Fair Value |  |
Held to Maturity, Due in one year or less | 47,269 |
Held to Maturity, Due after one year through five years | 199,266 |
Held to Maturity, Due after five years through ten years | 361,260 |
Held to Maturity, Due after ten years | 972,504 |
Held to Maturity, Securities, Debt Securities | 1,580,300 |
Held to Maturity, Total debt securities | $ 2,560,943 | 2,283,574
Ratio of Fair Value to Amortized Cost | 98.40% |
Private Label |  |
Amortized Cost |  |
Investment securities available for sale, amortized cost | $ 1,037 | 1,067
Fair Value |  |
Investment securities available for sale, at fair value | 1,031 | 1,059
Amortized Cost |  |
Held to Maturity Amortized Cost | 0 |
Fair Value |  |
Held to Maturity, Total debt securities | 0 |
GNMA Commercial Mortgage-Related Securities |  |
Amortized Cost |  |
Investment securities available for sale, amortized cost | 1,400,680 | 1,547,173
Fair Value |  |
Investment securities available for sale, at fair value | 1,348,282 | 1,513,277
Amortized Cost |  |
Held to Maturity Amortized Cost | 523,103 |
Fair Value |  |
Held to Maturity, Total debt securities | 507,813 |
Asset backed Securities |  |
Amortized Cost |  |
Investment securities available for sale, amortized cost | 298,263 |
Fair Value |  |
Investment securities available for sale, at fair value | 299,831 |
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 | 1,613 | 1,519
Fair Value |  |
Investment securities available for sale, at fair value | 1,613 | 1,632
Amortized Cost |  |
Held to Maturity Amortized Cost | 0 |
Fair Value |  |
Held to Maturity, Total debt securities | 0 |
FNMA and FHLMC | Residential Related Securities |  |
Amortized Cost |  |
Investment securities available for sale, amortized cost | 396,368 | 457,680
Fair Value |  |
Investment securities available for sale, at fair value | 396,709 | 464,768
Amortized Cost |  |
Held to Maturity Amortized Cost | 97,822 | 40,995
Fair Value |  |
Held to Maturity, Total debt securities | 95,707 | 40,904
GNMA | Residential Related Securities |  |
Amortized Cost |  |
Investment securities available for sale, amortized cost | 2,275,481 | 1,944,453
Fair Value |  |
Investment securities available for sale, at fair value | 2,210,189 | 1,913,350
Amortized Cost |  |
Held to Maturity Amortized Cost | 388,174 | 414,440
Fair Value |  |
Held to Maturity, Total debt securities | $ 377,123 | 410,740
GNMA | GNMA Commercial Mortgage-Related Securities |  |
Amortized Cost |  |
Held to Maturity Amortized Cost |  | 546,098
Fair Value |  |
Held to Maturity, Total debt securities |  | $ 539,888

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