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Summary of Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Detail) $ in Thousands | Dec. 31, 2017 USD ($)
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Available-for-Sale Securities: |  |
Due within one year | $ 259,617 | [1]
Due from one to five years | 963,589 | [1]
Due from five to ten years | 1,361,457 | [1]
Due after ten years | 914,230 | [1]
Total securities available for sale | 3,498,893 | [1]
Mortgage-Related Securities |  |
Available-for-Sale Securities: |  |
Due from one to five years | 883,138 | [2]
Due from five to ten years | 1,002,205 | [1]
Due after ten years | 674,618 | [1]
Total securities available for sale | $ 2,559,961 | [1]
Available-for-Sale Securities, Average Yield |  |
Due from one to five years, Average Yield | 3.32% | [1]
Due from five to ten years, Average Yield | 3.44% | [1]
Due after ten years, Average Yield | 3.09% | [1]
Total securities available for sale, Average Yield | 3.30% | [1]
U.S. Treasury and GSE Obligations |  |
Available-for-Sale Securities: |  |
Due within one year | $ 259,256 | [2]
Due from one to five years | 6,950 | [2]
Due from five to ten years | 283,883 | [1]
Due after ten years | 123,750 | [1]
Total securities available for sale | $ 673,839 | [1]
Available-for-Sale Securities, Average Yield |  |
Due within one year, Average Yield | 1.82% | [1]
Due from one to five years, Average Yield | 3.84% | [1]
Due from five to ten years, Average Yield | 3.08% | [1]
Due after ten years, Average Yield | 3.23% | [1]
Total securities available for sale, Average Yield | 3.22% | [1]
State, county, and municipal |  |
Available-for-Sale Securities: |  |
Due within one year | $ 148 | [2]
Due from one to five years | 291 | [2]
Due after ten years | 69,942 | [1]
Total securities available for sale | $ 70,381 | [1]
Available-for-Sale Securities, Average Yield |  |
Due within one year, Average Yield | 6.51% | [1],[3]
Due from one to five years, Average Yield | 6.63% | [1],[3]
Due after ten years, Average Yield | 2.88% | [1],[3]
Total securities available for sale, Average Yield | 2.90% | [1],[3]
Other Debt Securities |  |
Available-for-Sale Securities: |  |
Due from one to five years | $ 48,449 | [2]
Due from five to ten years | 31,253 | [1]
Due after ten years | 48,230 | [1]
Total securities available for sale | $ 127,932 | [1]
Available-for-Sale Securities, Average Yield |  |
Due from one to five years, Average Yield | 3.57% | [1]
Due from five to ten years, Average Yield | 8.37% | [1]
Due after ten years, Average Yield | 3.77% | [1]
Total securities available for sale, Average Yield | 4.82% | [1]
[1] | As equity securities have no contractual maturity, they have been excluded from this table.
[2] | (3) As equity securities have no contractual maturity, they have been excluded from this table.
[3] | Not presented on a tax-equivalent basis.

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