Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended									3 Months Ended
	Mar. 31, 2013 Y Security	Mar. 31, 2012	Dec. 31, 2012 Security	Dec. 31, 2012 Investment grade [Member]	Mar. 31, 2013 Trust Preferred Securities [Member] Securities	Mar. 31, 2013 Trust Preferred Securities [Member] Non-rated [Member]	Mar. 31, 2013 Trust preferred securities [Member]	Sep. 30, 2012 Trust preferred securities [Member]	Dec. 31, 2011 Trust preferred securities [Member]	Mar. 31, 2013 Trust preferred securities [Member] Zero percent yielding Freddie Mac and Fannie Mae perpetual preferred stock [Member]	Mar. 31, 2013 Single-issuer bank trust preferred securities [Member]	Dec. 31, 2012 Single-issuer bank trust preferred securities [Member]	Mar. 31, 2013 Pooled trust preferred securities [Member] Security	Dec. 31, 2012 Pooled trust preferred securities [Member] Securities	Mar. 31, 2013 Pooled trust preferred securities [Member] Non-investment grade [Member] Securities	Mar. 31, 2013 Pooled trust preferred securities [Member] Investment grade [Member] Securities	Mar. 31, 2013 Residential mortgage-backed securities [Member]	Dec. 31, 2012 Residential mortgage-backed securities [Member]	Dec. 31, 2012 Private label mortgage-backed securities [Member] Securities	Mar. 31, 2013 Private label mortgage-backed securities [Member] Non-investment grade [Member] Securities	Dec. 31, 2012 Private Label Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Private Label Residential Mortgage-Backed Securities [Member] Investment grade [Member]	Mar. 31, 2013 Perpetual Preferred Securities [Member] Security
Investment Securities [Line Items]
Held to maturity, fair value	$ 1,614,712,000		$ 1,657,950,000														$ 772,617,000	$ 838,116,000
Available for sale	955,270,000		807,816,000														568,323,000	510,154,000
Trading investment securities	22,127,000		22,157,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	84		74		9								3	3	2	1			2				2
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	56		34			4
Fair value of investments held to maturity pledged as collateral	836,800,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	3.2
Gross unrealized losses	19,358,000		19,479,000	3,000,000			1,900,000						4,600,000				5,008,000	3,359,000		1,500,000	477,000	3,500,000	1,600,000
Number of non-investment grade private label mortgage-backed securities																				1
Amortized Cost	957,997,000		813,474,000				16,500,000						17,400,000				567,697,000	506,695,000					10,000,000
Fair value							14,600,000						12,800,000
Unrealized losses, available-for-sale securities	19,358,000		19,479,000													3,000,000	5,008,000	3,359,000
Fair value of securities available for sale pledged as collateral	356,200,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	3.7
Other-than-temporarily impaired trust preferred securities, amortized cost	41,800,000
Other-than-temporarily impaired trust preferred securities, fair value	44,500,000
Impairment charge part of combined amortized cost of the securities								4,500,000	18,300,000
Gains from sales transactions										3,400,000
Preferred stock, amortized cost										941,000
Fair value of trading securities											22,100,000	22,200,000
Interest income on trading securities	$ 442,000	$ 442,000