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Summary of Portfolio of Securities Available for Sale (Detail) - USD ($) $ in Thousands | Jun. 30, 2017 | Dec. 31, 2016
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | $ 3,081,676 | [1] | $ 105,567
Gross Unrealized Gain |  | 102,937 | [1] | 1,980
Gross Unrealized Loss |  | 13,496 | [1] | 3,266
Fair Value |  | 3,171,117 | [1] | 104,281
Mortgage-Related Securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 2,540,172 |  |
Gross Unrealized Gain |  | 85,090 |  |
Gross Unrealized Loss |  | 1,014 |  |
Fair Value |  | 2,624,248 |  |
Mortgage-Related Securities | GSE certificates |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 1,941,943 | [2] | 7,786
Gross Unrealized Gain | [2] | 61,714 |  |
Gross Unrealized Loss |  | 1,014 | [2] | 460
Fair Value |  | 2,002,643 | [2] | 7,326
Mortgage-Related Securities | GSE CMOs |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost | [3] | 598,229 |  |
Gross Unrealized Gain | [3] | 23,376 |  |
Fair Value | [3] | 621,605 |  |
Other Securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 541,504 |  | 97,781
Gross Unrealized Gain |  | 17,847 |  | 1,980
Gross Unrealized Loss |  | 12,482 |  | 2,806
Fair Value |  | 546,869 |  | 96,955
Other Securities | Municipal bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 71,339 |  | 583
Gross Unrealized Gain |  | 113 |  | 48
Gross Unrealized Loss |  | 939 |  |
Fair Value |  | 70,513 |  | 631
Other Securities | Capital trust notes |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 75,206 |  | 9,458
Gross Unrealized Gain |  | 2,538 |  | 2
Gross Unrealized Loss |  | 11,319 |  | 2,217
Fair Value |  | 66,425 |  | 7,243
Other Securities | Preferred Stock (Par Value: $0.01): |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 15,293 |  | 70,866
Gross Unrealized Gain |  | 142 |  | 1,446
Gross Unrealized Loss |  |  |  | 328
Fair Value |  | 15,435 |  | 71,984
Other Securities | Mutual Funds and Common Stock |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 16,874 | [4] | 16,874
Gross Unrealized Gain |  | 471 | [4] | 484
Gross Unrealized Loss |  | 195 | [4] | 261
Fair Value |  | 17,150 | [4] | $ 17,097
Other Securities | U.S. Treasury obligations |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 200,021 |  |
Gross Unrealized Loss |  | 29 |  |
Fair Value |  | 199,992 |  |
Other Securities | GSE debentures |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 88,315 |  |
Gross Unrealized Gain |  | 2,919 |  |
Fair Value |  | 91,234 |  |
Other Securities | Corporate bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized Cost |  | 74,456 |  |
Gross Unrealized Gain |  | 11,664 |  |
Fair Value |  | $ 86,120 |  |
[1] | The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At June 30, 2017, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).
[2] | Government-sponsored enterprise.
[3] | Collateralized mortgage obligations.
[4] | Primarily consists of mutual funds that are Community Reinvestment Act-qualified investments.

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