Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012 Y Security	Dec. 31, 2011 Security	Dec. 31, 2010
Investment Securities [Line Items]
Held to maturity, fair value		$ 1,657,950,000	$ 2,027,197,000
Available for sale		807,816,000	566,520,000
Trading investment securities		22,157,000	21,938,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position		74	43
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		34	28
Fair value of investments held to maturity pledged as collateral		837,900,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years		4.2
Gross unrealized losses		19,479,000	49,745,000
Amortized Cost		813,474,000	598,837,000
Unrealized losses, available-for-sale securities		19,479,000	49,745,000
Fair value of securities available for sale pledged as collateral		371,300,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years		5.0
Additional estimated credit losses	4,500,000
Other-than-temporarily impaired trust preferred securities, amortized cost		41,800,000
Non-credit impairment charges (before taxes)		5,100,000
Fair value of securities		36,700,000
Other-than-temporary impairment charges attributable to credit on trust preferred securities		4,500,000	18,300,000
Recognized impairment charges		722,000
Gross gains on the early redemption		5,300,000	31,500,000
Interest income on trading securities		1,800,000	2,100,000	2,600,000
Junior Subordinated Debentures [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		8
Investment grade [Member] | Junior Subordinated Debentures [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		1
Non-investment grade [Member] | Junior Subordinated Debentures [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		2
Not rated [Member] | Junior Subordinated Debentures [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		5
Trust preferred securities [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position		8
Gross unrealized losses		5,200,000
Amortized Cost		16,500,000
Fair value		11,400,000
Impairment charge part of combined amortized cost of the securities			18,300,000
Residential mortgage-backed securities [Member]
Investment Securities [Line Items]
Trading investment securities			141,100,000
Gross unrealized losses		3,400,000
Gross gains on sales transactions			651,700,000
Trust Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position		10
Single-issuer bank trust preferred securities
Investment Securities [Line Items]
Fair value of trading securities		22,200,000	21,900,000
Pooled trust preferred securities [Member]
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position		3
Gross unrealized losses		5,600,000
Amortized Cost		17,500,000
Fair value		11,900,000
Other-than-temporarily impaired trust preferred securities, amortized cost		5,400,000
Other-than-temporarily impaired trust preferred securities, fair value		3,600,000
Pooled trust preferred securities [Member] | Investment grade [Member]
Investment Securities [Line Items]
Unrealized losses, available-for-sale securities		3,800,000
Private label mortgage-backed securities [Member]
Investment Securities [Line Items]
Gross unrealized losses		1,600,000
Number of private label mortgage-backed securities		2
Other-than-temporarily impaired mortgage-backed securities, amortized cost		31,700,000
Other-than-temporarily impaired mortgage-backed securities, fair value		31,400,000
Private label mortgage-backed securities [Member] | Investment grade [Member]
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position		1
Gross unrealized losses		526,000
Private label mortgage-backed securities [Member] | Residential mortgage-backed securities [Member]
Investment Securities [Line Items]
Gross unrealized losses		1,800,000
Private label mortgage-backed securities [Member] | Residential mortgage-backed securities [Member] | Investment grade [Member]
Investment Securities [Line Items]
Gross unrealized losses		1,300,000
Perpetual Preferred Securities
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position		2
Gross unrealized losses		1,700,000
Amortized Cost		$ 10,000,000