Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2015		Dec. 31, 2014
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	$ 21,577	[1]	$ 49,664	[2]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	42,208		53,721
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	1,147		364
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	4,779		20,625
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,662		2,099
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	46,987		74,346
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	3,809		2,463
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	785,665		13,735
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	2,314		195
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	1,227,835		2,587,594
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	19,263		49,469
Temporarily Impaired Held-to-Maturity, Total Fair Value	2,013,500		2,601,329
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	21,577		49,664
Debt Securities | GSE debentures
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	558,816
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	355
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	1,194,688		2,204,399
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	4,134		32,920
Temporarily Impaired Held-to-Maturity, Total Fair Value	1,753,504		2,204,399
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	4,489		32,920
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	159,903
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	541
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	11,852		242,909
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	220		3,838
Temporarily Impaired Held-to-Maturity, Total Fair Value	171,755		242,909
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	761		3,838
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value			72,209
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss			711
Temporarily Impaired Held-to-Maturity, Total Fair Value			72,209
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss			711
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	42,324		13,735
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	1,039		195
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value			43,058
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss			832
Temporarily Impaired Held-to-Maturity, Total Fair Value	42,324		56,793
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	1,039		1,027
Debt Securities | Capital trust notes
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	24,622
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	379
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	21,295		25,019
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	14,909		11,168
Temporarily Impaired Held-to-Maturity, Total Fair Value	45,917		25,019
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	15,288		11,168
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	1,970
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	30
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	4,779		5,451
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,662		1,980
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	6,749		5,451
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,692		1,980
Equity securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	40,238		53,721
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	1,117		364
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value			15,174
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss			119
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	40,238		68,895
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 1,117		$ 483

[1] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At September 30, 2015, the non-credit portion of OTTI recorded in AOCL was $8.7 million (before tax).

[2] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2014, the non-credit portion of OTTI recorded in AOCL was $8.8 million (before taxes).