Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	$ 177,954,000	[1]	$ 14,002,000	[2]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	94,295,000		60,655,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	1,103,000		155,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	6,171,000		33,413,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	3,116,000		7,073,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	100,466,000		94,068,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	4,219,000		7,228,000
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	3,488,976,000		2,238,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	166,520,000		5,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	34,721,000		32,148,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	11,434,000		13,997,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	3,523,697,000		34,386,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	177,954,000		14,002,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	15,325,000		45,393,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	140,000		125,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	5,177,000		4,424,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,435,000		4,160,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	20,502,000		49,817,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,575,000		4,285,000
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	896,722,000		2,238,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	34,912,000		5,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	896,722,000		2,238,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	34,912,000		5,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value			297,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss			5,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	198,000		53,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,000		1,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	198,000		350,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,000		6,000
Debt Securities | Private label CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	13,370,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	95,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	13,370,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	95,000
Debt Securities | State, county, and municipal
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value			45,096,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss			120,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value			45,096,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss			120,000
Debt Securities | Capital trust notes
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	24,441,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	560,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	34,721,000		32,148,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	11,434,000		13,997,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	59,162,000		32,148,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	11,994,000		13,997,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	1,955,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	45,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	4,979,000		4,371,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,433,000		4,159,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	6,934,000		4,371,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,478,000		4,159,000
Debt Securities | GSE debentures
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	2,120,642,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	116,622,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	2,120,642,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	116,622,000
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	390,518,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	11,169,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	390,518,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	11,169,000
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	56,653,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	3,257,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	56,653,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	3,257,000
Equity Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	78,970,000		15,262,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	963,000		30,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	994,000		28,989,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	681,000	[3]	2,913,000	[4]
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	79,964,000		44,251,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 1,644,000		$ 2,943,000

[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 June 30, 2013, the non-credit portion of OTTI recorded in AOCL was $9.2 million (before taxes).

[2] At December 31, 2012, the non-credit portion of OTTI recorded in AOCL was $21.6 million (before taxes).

[3] The twelve months or longer unrealized losses on equity securities of $681,000 at June 30, 2013 relate to an investment in a financial institution. The principal balance of the investment was $1.7 million at that date.

[4] The twelve months or longer unrealized losses on equity securities of $2.9 million at December 31, 2012 relate to available-for-sale equity securities that consisted of a large cap equity fund and investments in certain financial institutions. The principal balance of the large cap equity fund was $30.2 million and the twelve months or longer unrealized loss was $2.2 million at that date. The principal balance of investments in financial institutions totaled $1.7 million and the twelve months or longer unrealized loss was $709,000 at that date.