Summary of Held-to-Maturity and Available-for-Sale Securities Having Continuous Unrealized Loss Position (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	$ 246,548,000	[1]	$ 14,002,000	[2]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	135,621,000		60,655,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	5,244,000		155,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	6,659,000		33,413,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	2,603,000		7,073,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	142,280,000		94,068,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	7,847,000		7,228,000
Debt Securities
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	4,012,799,000		2,238,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	235,780,000		5,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	35,393,000		32,148,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	10,768,000		13,997,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	4,048,192,000		34,386,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	246,548,000		14,002,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	60,104,000		45,393,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	786,000		125,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	5,613,000		4,424,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	1,973,000		4,160,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	65,717,000		49,817,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,759,000		4,285,000
Debt Securities | GSE certificates
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	1,087,114,000		2,238,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	48,066,000		5,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	1,087,114,000		2,238,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	48,066,000		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	167,000		53,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	3,000		1,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	167,000		350,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	3,000		6,000
Debt Securities | Private label CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	12,255,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	62,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	12,255,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	62,000
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	24,581,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	419,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Fair Value	35,393,000		32,148,000
Temporarily Impaired Held-to-Maturity, Twelve Months or Longer Unrealized Loss	10,768,000		13,997,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	59,974,000		32,148,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	11,187,000		13,997,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	1,966,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	33,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	5,446,000		4,371,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	1,970,000		4,159,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	7,412,000		4,371,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	2,003,000		4,159,000
Debt Securities | GSE debentures
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	2,344,708,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	170,695,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	2,344,708,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	170,695,000
Debt Securities | GSE CMOs
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	500,367,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	12,890,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	500,367,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	12,890,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	45,883,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	691,000
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	45,883,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	691,000
Debt Securities | Municipal bonds
Schedule of Investments [Line Items]
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Fair Value	56,029,000
Temporarily Impaired Held-to-Maturity, Less than Twelve Months Unrealized Loss	3,710,000
Temporarily Impaired Held-to-Maturity, Total Fair Value	56,029,000
Temporarily Impaired Held-to-Maturity, Total Unrealized Loss	3,710,000
Equity Securities
Schedule of Investments [Line Items]
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Fair Value	75,517,000		15,262,000
Temporarily Impaired Available-for-Sale Securities, Less than Twelve Months Unrealized Loss	4,458,000		30,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Fair Value	1,046,000		28,989,000
Temporarily Impaired Available-for-Sale Securities, Twelve Months or Longer Unrealized Loss	630,000	[3]	2,913,000	[4]
Temporarily Impaired Available-for-Sale Securities, Total Fair Value	76,563,000		44,251,000
Temporarily Impaired Available-for-Sale Securities, Total Unrealized Loss	$ 5,088,000		$ 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 September 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 $630,000 at September 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.