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Summary of Portfolio of Securities Held to Maturity (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | $ 3,650,663 |  | $ 3,721,368 | [1]
Carrying Amount | 3,642,104 |  | 3,712,776 | [1]
Gross Unrealized Gain | 121,015 |  | 117,373 | [1]
Gross Unrealized Loss | 13,070 |  | 16,190 | [1]
Fair Value | 3,750,049 |  | 3,813,959 | [1]
Mortgage-Related Securities |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 3,142,193 |  | 3,212,563 |
Carrying Amount | 3,142,193 |  | 3,212,563 |
Gross Unrealized Gain | 103,116 |  | 101,326 |
Gross Unrealized Loss | 1,297 |  | 2,456 |
Fair Value | 3,244,012 |  | 3,311,433 |
Mortgage-Related Securities | GSE certificates |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 2,170,706 |  | 2,193,489 |
Carrying Amount | 2,170,706 |  | 2,193,489 |
Gross Unrealized Gain | 70,183 |  | 64,431 |
Gross Unrealized Loss | 1,078 |  | 2,399 |
Fair Value | 2,239,811 |  | 2,255,521 |
Mortgage-Related Securities | GSE CMOs |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 971,487 | [2] | 1,019,074 |
Carrying Amount | 971,487 | [2] | 1,019,074 |
Gross Unrealized Gain | 32,933 | [2] | 36,895 |
Gross Unrealized Loss | 219 | [2] | 57 |
Fair Value | 1,004,201 | [2] | 1,055,912 |
Other Securities |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 508,470 |  | 508,805 |
Carrying Amount | 499,911 |  | 500,213 |
Gross Unrealized Gain | 17,899 |  | 16,047 |
Gross Unrealized Loss | 11,773 |  | 13,734 |
Fair Value | 506,037 |  | 502,526 |
Other Securities | U.S. Treasury obligations |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 200,158 |  | 200,293 |
Carrying Amount | 200,158 |  | 200,293 |
Gross Unrealized Loss | 103 |  | 73 |
Fair Value | 200,055 |  | 200,220 |
Other Securities | GSE debentures |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 88,387 |  | 88,457 |
Carrying Amount | 88,387 |  | 88,457 |
Gross Unrealized Gain | 3,565 |  | 3,836 |
Fair Value | 91,952 |  | 92,293 |
Other Securities | Corporate bonds |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 74,337 |  | 74,217 |
Carrying Amount | 74,337 |  | 74,217 |
Gross Unrealized Gain | 11,079 |  | 9,549 |
Fair Value | 85,416 |  | 83,766 |
Other Securities | Municipal bonds |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 71,297 |  | 71,554 |
Carrying Amount | 71,297 |  | 71,554 |
Gross Unrealized Gain | 533 |  |  |
Gross Unrealized Loss | 1,474 |  | 1,789 |
Fair Value | 70,356 |  | 69,765 |
Other Securities | Capital trust notes |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Amortized Cost | 74,291 |  | 74,284 |
Carrying Amount | 65,732 |  | 65,692 |
Gross Unrealized Gain | 2,722 |  | 2,662 |
Gross Unrealized Loss | 10,196 |  | 11,872 |
Fair Value | $ 58,258 |  | $ 56,482 |
[1] | Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2016, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).
[2] | Collateralized mortgage obligations.

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