Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended					1 Months Ended			3 Months Ended																9 Months Ended
	Sep. 30, 2013 Security Y	Sep. 30, 2012	Sep. 30, 2013 Security Y	Sep. 30, 2012	Dec. 31, 2012 Security	Sep. 30, 2013 Corporate and Other Debt Securities [Member]	Sep. 30, 2013 Trust Preferred Securities [Member] Previously Other-Than-Temporarily Impaired Securities [Member]	Oct. 31, 2013 Subsequent event [Member]	Sep. 30, 2013 Trust Preferred Securities [Member] Securities	Sep. 30, 2013 Trust Preferred Securities [Member] Non-Rated [Member]	Sep. 30, 2012 Trust Preferred Securities [Member]	Sep. 30, 2013 Trust Preferred Securities [Member]	Dec. 31, 2011 Trust Preferred Securities [Member]	Sep. 30, 2013 Single-Issuer Bank Trust Preferred Securities [Member]	Dec. 31, 2012 Single-Issuer Bank Trust Preferred Securities [Member]	Sep. 30, 2013 Pooled Trust Preferred Securities [Member] Securities	Dec. 31, 2012 Pooled Trust Preferred Securities [Member] Securities	Sep. 30, 2013 Pooled Trust Preferred Securities [Member] Investment Grade [Member] Securities	Sep. 30, 2013 Pooled Trust Preferred Securities [Member] Non-Investment Grade [Member] Securities	Sep. 30, 2013 Perpetual Preferred Securities [Member] Security	Sep. 30, 2013 Three Private Label Mortgage-Backed Securities [Member]	Sep. 30, 2013 Three Private Label Mortgage-Backed Securities [Member] Investment Grade [Member] Securities	Sep. 30, 2013 Three Private Label Mortgage-Backed Securities [Member] Previously Other-Than-Temporarily Impaired Securities [Member] Investment Grade [Member] Securities	Sep. 30, 2013 Several Investment Grade Residential Mortgage-Backed Securities [Member] Investment Grade [Member]	Sep. 30, 2013 Obligations of States and Political Subdivisions [Member]	Dec. 31, 2012 Obligations of States and Political Subdivisions [Member]	Sep. 30, 2013 Obligations of States and Political Subdivisions [Member] Other Than Temporarily Impaired Securities [Member]
Investment Securities [Line Items]
Held to maturity, fair value	$ 1,701,492,000		$ 1,701,492,000		$ 1,657,950,000																				$ 523,371,000	$ 531,966,000
Available for sale	910,809,000		910,809,000		807,816,000		52,300,000					16,300,000				10,700,000					25,900,000				37,553,000	16,627,000	18,000,000
Fair value of trading securities	14,270,000		14,270,000		22,157,000									14,300,000	22,200,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	108		108		74				10			10				3	3	1	2	2
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	104		104		34					4
Fair value of investments held to maturity pledged as collateral	769,000,000		769,000,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	5.8		5.8
Gross unrealized losses	39,232,000		39,232,000		19,479,000	2,000,000						255,000				3,100,000				1,500,000		4,400,000	1,000,000	10,500,000	2,335,000
Number of investment grade private label mortgage-backed securities																						3	3
Amortized Cost	934,704,000		934,704,000		813,474,000		47,200,000					16,500,000				13,800,000				10,000,000	26,700,000				39,285,000	16,210,000	18,400,000
Gross unrealized losses	39,232,000		39,232,000		19,479,000													1,800,000							2,335,000		11,400,000
Fair value of securities available for sale pledged as collateral	404,100,000		404,100,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	4.1		4.1
Investment carrying value																											562,100,000
Investment carrying value percentage																											55.00%
Credit factors risk percentage			25.00%
Other-than-temporarily impaired trust preferred securities, amortized cost			41,800,000
Other-than-temporarily impaired trust preferred securities, fair value	48,300,000		48,300,000
Impairment charge part of combined amortized cost of the securities											4,500,000		18,300,000
Sale of net proceeds of debt securities								52,500,000
Realized gain on securities								10,700,000
Gains on securities transactions, net	9,000	1,496,000	4,008,000	2,543,000							5,300,000
Interest income on trading securities	$ 290,000	$ 442,000	$ 1,100,000	$ 1,300,000