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Summary of Amortized Cost of Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Available-for-Sale Debt Securities: |  |  |  |
Due within one year | [1] | $ 151 |  |
Due from one to five years | [1] | 1,463,371 |  |
Due from five to ten years | [1] | 1,605,017 |  |
Due after ten years | [1] | 1,695,744 |  |
Total debt securities available for sale |  | 4,764,283 | [1] | $ 3,531,427
Mortgage-Related Securities |  |  |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years | [1] | 1,378,471 |  |
Due from five to ten years | [1] | 326,275 |  |
Due after ten years | [1] | 1,106,740 |  |
Total debt securities available for sale | [1] | $ 2,811,486 |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years, Average Yield | [1] | 3.31% |  |
Due from five to ten years, Average Yield | [1] | 3.44% |  |
Due after ten years, Average Yield | [1] | 3.19% |  |
Total debt securities available for sale | [1] | 3.28% |  |
U.S. Treasury and GSE Obligations |  |  |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years | [1] | $ 6,950 |  |
Due from five to ten years | [1] | 927,006 |  |
Due after ten years | [1] | 109,971 |  |
Total debt securities available for sale | [1] | $ 1,043,927 |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years, Average Yield | [1] | 3.84% |  |
Due from five to ten years, Average Yield | [1] | 3.33% |  |
Due after ten years, Average Yield | [1] | 3.68% |  |
Total debt securities available for sale | [1] | 3.37% |  |
State, county, and municipal |  |  |  |
Available-for-Sale Debt Securities: |  |  |  |
Due within one year | [1] | $ 149 |  |
Due from one to five years | [1] | 294 |  |
Due after ten years | [1] | 68,833 |  |
Total debt securities available for sale | [1] | $ 69,276 |  |
Available-for-Sale Debt Securities: |  |  |  |
Due within one year, Average Yield | [1],[2] | 6.51% |  |
Due from one to five years, Average Yield | [1],[2] | 6.63% |  |
Due after ten years, Average Yield | [1],[2] | 2.88% |  |
Total debt securities available for sale | [1],[2] | 2.90% |  |
Other Debt Securities |  |  |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years | [1],[3] | $ 78,787 |  |
Due from five to ten years | [1],[3] | 367,115 |  |
Due after ten years | [1],[3] | 436,047 |  |
Total debt securities available for sale | [1],[3] | $ 881,949 |  |
Available-for-Sale Debt Securities: |  |  |  |
Due from one to five years, Average Yield | [1] | 3.64% |  |
Due from five to ten years, Average Yield | [1] | 4.02% |  |
Due after ten years, Average Yield | [1] | 3.23% |  |
Total debt securities available for sale | [1] | 3.60% |  |
[1] | As equity securities have no contractual maturity, they have been excluded from this table.
[2] | Not presented on a tax-equivalent basis.
[3] | Includes corporate bonds, capital trust notes, and asset-backed securities.

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