Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	$ 1,671,447	$ 2,054,583
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	18,617	40,139
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	627,545	759,881
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	14,790	22,547
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	2,298,992	2,814,464
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	33,407	62,686
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	396,930	576,970
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	3,718	10,598
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	7,542	232,969
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	45	5,363
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	404,472	809,939
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	3,763	15,961
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	609,502	465,779
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	2,582	1,892
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	133,955	99,050
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	959	2,348
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	743,457	564,829
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	3,541	4,240
Debt Securities | U.S. Treasury obligations
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	11,917
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	11,917
Debt Securities | GSE debentures
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	297,179	276,113
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	3,916	2,629
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	138,189	329,372
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	1,396	6,359
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	435,368	605,485
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	5,312	8,988
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value		5,876
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss		21
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	9,349	48,837
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	475	2,542
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	9,349	54,713
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	475	2,563
Debt Securities | Capital trust notes
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	37,525	38,360
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	6,306	5,422
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	37,525	38,360
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	6,306	5,422
Debt Securities | Asset-backed Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	256,619	69,166
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	7,701	430
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	116,635
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	3,154
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	373,254	69,166
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	10,855	430
Debt Securities | Corporate Bond Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	99,300	642,843
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	700	23,105
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	172,717
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,282
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	272,017	642,843
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,982	23,105
Equity securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value		17,836
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss		1,464
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	11,633	11,293
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	173	513
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	11,633	29,129
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 173	$ 1,977