Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012 Year Security	Jun. 30, 2011	Jun. 30, 2012 Year Security	Jun. 30, 2011	Dec. 31, 2011 Security
Investment Securities [Line Items]
Held to maturity, fair value	$ 1,860,722,000		$ 1,860,722,000		$ 2,027,197,000
Available for sale	688,788,000		688,788,000		566,520,000
Trading investment securities	22,039,000		22,039,000		21,938,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	69		69		43
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	33		33		28
Fair value of investments held to maturity pledged as collateral	1,000,000,000		1,000,000,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	3.2		3.2
Unrealized losses, available-for-sale securities	(23,694,000)		(23,694,000)		(49,745,000)
Unrealized losses, available-for-sale securities	23,694,000		23,694,000		49,745,000
Amortized Cost	691,602,000		691,602,000		598,837,000
Fair value of securities available for sale pledged as collateral	378,000,000		378,000,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	3.8		3.8
Impairment losses on securities	550,000	825,000	550,000	825,000
Other-than-temporarily impaired trust preferred securities, amortized cost			46,400,000		22,900,000
Non-credit impairment charges (before taxes)			3,800,000
Other-than-temporarily impaired mortgage-backed securities, amortized cost			45,100,000
Other-than-temporarily impaired mortgage-backed securities, fair value	43,200,000		43,200,000
Interest income on trading securities	462,000	500,000	884,000	1,100,000
Trust Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	16		16
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	10		10
Single issuer trust preferred securities
Investment Securities [Line Items]
Held to maturity, fair value	174,469,000		174,469,000		174,753,000
Unrealized losses, available-for-sale securities	5,300,000		5,300,000
Amortized Cost	19,000,000		19,000,000
Fair value	13,700,000		13,700,000
Impairment losses on securities					18,300,000
Single issuer trust preferred securities | Investment Grade
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	3		3
Single issuer trust preferred securities | Non-Investment Grade
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	2		2
Single issuer trust preferred securities | Not-Rated
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	5		5
Single-issuer bank trust preferred securities
Investment Securities [Line Items]
Fair value of trading securities	22,000,000		22,000,000		21,900,000
Other Debt Obligations [Member]
Investment Securities [Line Items]
Unrealized losses, available-for-sale securities	8,500,000		8,500,000
Pooled Trust Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	3		3
Amortized Cost	20,000,000		20,000,000
Fair value	11,500,000		11,500,000
Other-than-temporarily impaired trust preferred securities, amortized cost			5,400,000
Other-than-temporarily impaired trust preferred securities, fair value	3,400,000		3,400,000
Pooled Trust Preferred Securities | Investment Grade
Investment Securities [Line Items]
Unrealized losses, available-for-sale securities	6,500,000		6,500,000
Perpetual Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	2		2
Unrealized losses, available-for-sale securities	2,600,000		2,600,000
Amortized Cost	10,000,000		10,000,000
Mortgage-Backed Securities
Investment Securities [Line Items]
Available for sale	430,019,000		430,019,000		310,137,000
Unrealized losses, available-for-sale securities	(4,612,000)		(4,612,000)		(5,444,000)
Unrealized losses, available-for-sale securities	4,612,000		4,612,000		5,444,000
Amortized Cost	424,524,000		424,524,000		304,631,000
Private Label Mortgage-Backed Securities
Investment Securities [Line Items]
Unrealized losses, available-for-sale securities	2,000,000		2,000,000
Number of private label mortgage-backed securities	3		3
Unrealized losses, available-for-sale securities	$ 2,600,000		$ 2,600,000
Private Label Mortgage-Backed Securities | Investment Grade
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	1		1