Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	$ 22,470	[1]	$ 49,664	[2]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value			53,721
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss			364
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	5,955		20,625
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,542		2,099
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	5,955		74,346
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,542		2,463
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	1,033,229		13,735
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	4,646		195
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	1,450,728		2,587,594
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	17,824		49,469
Temporarily Impaired Held-to-Maturity, Total Fair Value	2,483,957		2,601,329
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	22,470		49,664
Debt Securities | GSE debentures
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	809,531
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	2,412
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	1,392,128		2,204,399
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	6,692		32,920
Temporarily Impaired Held-to-Maturity, Total Fair Value	2,201,659		2,204,399
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	9,104		32,920
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	165,674
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	1,882
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	13,233		242,909
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	198		3,838
Temporarily Impaired Held-to-Maturity, Total Fair Value	178,907		242,909
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	2,080		3,838
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	20,102		72,209
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	6		711
Temporarily Impaired Held-to-Maturity, Total Fair Value	20,102		72,209
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	6		711
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	58,024		13,735
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	352		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	58,024		56,793
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	352		1,027
Debt Securities | Capital trust notes
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	25,265		25,019
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	10,928		11,168
Temporarily Impaired Held-to-Maturity, Total Fair Value	25,265		25,019
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	10,928		11,168
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	4,964		5,451
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,471		1,980
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	4,964		5,451
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,471		1,980
Equity securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value			53,721
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss			364
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	991		15,174
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	71		119
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	991		68,895
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 71		$ 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 March 31, 2015, the non-credit portion of OTTI recorded in AOCL was $8.8 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).