Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	$ 982,071	$ 1,671,447
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	55,115	21,770
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	685,094	627,545
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	64,858	11,637
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	1,667,165	2,298,992
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	119,973	33,407
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	2,061	396,930
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	2	3,718
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value		7,542
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss		45
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	2,061	404,472
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2	3,763
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	314,957	609,502
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	2,795	2,582
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	191,806	133,955
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	3,018	959
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	506,763	743,457
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	5,813	3,541
Debt Securities | U.S. Treasury obligations
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	9,997	11,917
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	3
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	9,997	11,917
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	3
Debt Securities | U. S. Government agency and GSE obligations
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value		297,179
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss		3,916
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value		138,189
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss		1,396
Temporarily Impaired Available-for-Sale Securities, Total Fair Value		435,368
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss		5,312
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	9,156	9,349
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	614	475
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	9,156	9,349
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	614	475
Debt Securities | Capital trust notes
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	42,500
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	4,349
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	33,385	37,525
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	10,459	6,306
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	75,885	37,525
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	14,808	6,306
Debt Securities | Asset-backed Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	124,435	256,619
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	7,341	10,854
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	230,949	116,635
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	20,565
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	355,384	373,254
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	27,906	10,854
Debt Securities | Corporate Bond Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	473,280	99,300
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	40,174	700
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	219,798	172,717
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	30,202	2,283
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	693,078	272,017
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	70,376	2,983
Equity Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	14,841
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	451
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value		11,633
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss		173
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	14,841	11,633
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 451	$ 173