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Summary of Portfolio of Securities Available for Sale (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | $ 5,660,418 | $ 3,464,279 | [1]
Gross Unrealized Gain |  | 46,339 | 81,594 | [1]
Gross Unrealized Loss |  | 62,686 | 14,446 | [1]
Fair Value |  | 5,644,071 | 3,531,427 | [1]
Mortgage-Related Securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 2,953,957 | 2,559,961 |
Gross Unrealized Gain |  | 26,526 | 60,810 |
Gross Unrealized Loss |  | 20,201 | 2,025 |
Fair Value |  | 2,960,282 | 2,618,746 |
Mortgage-Related Securities | GSE certificates |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 1,705,336 | 2,023,677 |
Gross Unrealized Gain |  | 18,146 | 46,364 |
Gross Unrealized Loss |  | 15,961 | 1,199 |
Fair Value |  | 1,707,521 | 2,068,842 |
Mortgage-Related Securities | GSE CMOs |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 1,248,621 | 536,284 |
Gross Unrealized Gain |  | 8,380 | 14,446 |
Gross Unrealized Loss |  | 4,240 | 826 |
Fair Value |  | 1,252,761 | 549,904 |
Other Securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 904,318 |
Gross Unrealized Gain |  |  | 20,784 |
Gross Unrealized Loss |  |  | 12,421 |
Fair Value |  |  | 912,681 |
Other Securities | U.S. Treasury obligations |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 199,960 |
Gross Unrealized Gain |  |  | 0 |
Gross Unrealized Loss |  |  | 62 |
Fair Value |  |  | 199,898 |
Other Securities | GSE debentures |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 473,879 |
Gross Unrealized Gain |  |  | 2,044 |
Gross Unrealized Loss |  |  | 2,665 |
Fair Value |  |  | 473,258 |
Other Securities | Corporate bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 79,702 |
Gross Unrealized Gain |  |  | 11,073 |
Gross Unrealized Loss |  |  | 0 |
Fair Value |  |  | 90,775 |
Other Securities | Municipal bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 70,381 |
Gross Unrealized Gain |  |  | 540 |
Gross Unrealized Loss |  |  | 801 |
Fair Value |  |  | 70,120 |
Other Securities | Capital trust notes |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 48,230 |
Gross Unrealized Gain |  |  | 6,498 |
Gross Unrealized Loss |  |  | 8,632 |
Fair Value |  |  | 46,096 |
Other Securities | Preferred stock |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  |  | 15,292 |
Gross Unrealized Gain |  |  | 142 |
Gross Unrealized Loss |  |  | 0 |
Fair Value |  |  | 15,434 |
Other Securities | Mutual Funds and Common Stock |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost | [2] |  | 16,874 |
Gross Unrealized Gain | [2] |  | 487 |
Gross Unrealized Loss | [2] |  | 261 |
Fair Value | [2] |  | $ 17,100 |
Equity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 32,162 |  |
Gross Unrealized Gain |  | 366 |  |
Gross Unrealized Loss |  | 1,977 |  |
Fair Value |  | 30,551 |  |
Equity Securities [Member] | Preferred stock |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 15,292 |  |
Gross Unrealized Gain |  | 0 |  |
Gross Unrealized Loss |  | 1,446 |  |
Fair Value |  | 13,846 |  |
Equity Securities [Member] | Mutual Funds and Common Stock |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost | [2] | 16,870 |  |
Gross Unrealized Gain | [2] | 366 |  |
Gross Unrealized Loss | [2] | 531 |  |
Fair Value | [2] | 16,705 |  |
Debt Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 2,674,299 |  |
Gross Unrealized Gain |  | 19,447 |  |
Gross Unrealized Loss |  | 40,508 |  |
Fair Value |  | 2,653,238 |  |
Debt Securities [Member] | GSE debentures |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 1,334,549 |  |
Gross Unrealized Gain |  | 3,366 |  |
Gross Unrealized Loss |  | 8,988 |  |
Fair Value |  | 1,328,927 |  |
Debt Securities [Member] | Corporate bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 836,153 |  |
Gross Unrealized Gain |  | 8,667 |  |
Gross Unrealized Loss |  | 23,105 |  |
Fair Value |  | 821,715 |  |
Debt Securities [Member] | Municipal bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 68,551 |  |
Gross Unrealized Gain |  | 195 |  |
Gross Unrealized Loss |  | 2,563 |  |
Fair Value |  | 66,183 |  |
Debt Securities [Member] | Capital trust notes |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 48,278 |  |
Gross Unrealized Gain |  | 6,435 |  |
Gross Unrealized Loss |  | 5,422 |  |
Fair Value |  | 49,291 |  |
Debt Securities [Member] | Asset-backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost | [3] | 386,768 |  |
Gross Unrealized Gain | [3] | 784 |  |
Gross Unrealized Loss | [3] | 430 |  |
Fair Value | [3] | 387,122 |  |
Mortgage Backed Securities And Other Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost | [4] | 5,628,256 |  |
Gross Unrealized Gain | [4] | 45,973 |  |
Gross Unrealized Loss | [4] | 60,709 |  |
Fair Value | [4] | $ 5,613,520 |  |
[1] | The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At December 31, 2017, the non-credit portion of OTTI recorded in AOCL was $8.6 million before taxes.
[2] | Primarily consists of mutual funds that are CRA-qualified investments.
[3] | The underlying assets of the asset-backed securities are substantially guaranteed by the U.S. Government.
[4] | The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At December 31, 2018, the non-credit portion of OTTI recorded in AOCL was $8.6 million before taxes.

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