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Summary of Portfolio of Securities Available for Sale (Detail) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | $ 5,841,796 | $ 5,660,418
Gross Unrealized Gain |  | 77,498 | 46,339
Gross Unrealized Loss |  | 33,407 | 62,686
Fair Value |  | 5,885,887 | 5,644,071
Mortgage-related Securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 3,313,757 | 2,953,957
Gross Unrealized Gain |  | 47,282 | 26,526
Gross Unrealized Loss |  | 7,304 | 20,201
Fair Value |  | 3,353,735 | 2,960,282
Mortgage-related Securities | GSE certificates |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 1,530,317 | 1,705,336
Gross Unrealized Gain |  | 26,069 | 18,146
Gross Unrealized Loss |  | 3,763 | 15,961
Fair Value |  | 1,552,623 | 1,707,521
Mortgage-related Securities | GSE CMOs |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 1,783,440 | 1,248,621
Gross Unrealized Gain |  | 21,213 | 8,380
Gross Unrealized Loss |  | 3,541 | 4,240
Fair Value |  | 1,801,112 | 1,252,761
Equity Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 32,163 | 32,162
Gross Unrealized Gain |  | 840 | 366
Gross Unrealized Loss |  | 173 | 1,977
Fair Value |  | 32,830 | 30,551
Equity Securities [Member] | Preferred stock |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 15,292 | 15,292
Gross Unrealized Gain |  | 122 |
Gross Unrealized Loss |  |  | 1,446
Fair Value |  | 15,414 | 13,846
Equity Securities [Member] | Mutual Funds and Common Stock |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | [1] | 16,871 | 16,870
Gross Unrealized Gain | [1] | 718 | 366
Gross Unrealized Loss | [1] | 173 | 531
Fair Value | [1] | 17,416 | 16,705
Debt Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 2,495,876 | 2,674,299
Gross Unrealized Gain |  | 29,376 | 19,447
Gross Unrealized Loss |  | 25,930 | 40,508
Fair Value |  | 2,499,322 | 2,653,238
Debt Securities [Member] | U.S. Treasury obligations |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 41,820 |
Gross Unrealized Gain |  | 19 |
Fair Value |  | 41,839 |
Debt Securities [Member] | GSE debentures |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 1,093,845 | 1,334,549
Gross Unrealized Gain |  | 5,707 | 3,366
Gross Unrealized Loss |  | 5,312 | 8,988
Fair Value |  | 1,094,240 | 1,328,927
Debt Securities [Member] | Corporate bonds |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 854,195 | 836,153
Gross Unrealized Gain |  | 15,970 | 8,667
Gross Unrealized Loss |  | 2,983 | 23,105
Fair Value |  | 867,182 | 821,715
Debt Securities [Member] | Municipal bonds |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 26,808 | 68,551
Gross Unrealized Gain |  | 559 | 195
Gross Unrealized Loss |  | 475 | 2,563
Fair Value |  | 26,892 | 66,183
Debt Securities [Member] | Capital trust notes |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost |  | 95,100 | 48,278
Gross Unrealized Gain |  | 7,121 | 6,435
Gross Unrealized Loss |  | 6,306 | 5,422
Fair Value |  | 95,915 | 49,291
Debt Securities [Member] | Asset-backed Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | [2] | 384,108 | 386,768
Gross Unrealized Gain | [2] |  | 784
Gross Unrealized Loss | [2] | 10,854 | 430
Fair Value | [2] | 373,254 | 387,122
Mortgage Backed Securities And Other Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | [3] | 5,809,633 | 5,628,256
Gross Unrealized Gain | [3] | 76,658 | 45,973
Gross Unrealized Loss | [3] | 33,234 | 60,709
Fair Value | [3] | $ 5,853,057 | $ 5,613,520
[1] | Primarily consists of mutual funds that are CRA-qualified investments.
[2] | The underlying assets of the asset-backed securities are substantially guaranteed by the U.S. Government.
[3] | The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At December 31, 2019, the non-credit portion of OTTI recorded in AOCL was $0.0 million before taxes.

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