Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended						3 Months Ended	6 Months Ended													6 Months Ended
	Jun. 30, 2013 Security Y	Jun. 30, 2012	Jun. 30, 2013 Security Y	Jun. 30, 2012	Dec. 31, 2012 Security	Jun. 30, 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]	Jun. 30, 2013 Trust preferred securities [Member] Zero percent yielding Freddie Mac and Fannie Mae perpetual preferred stock [Member]	Jun. 30, 2013 Trust Preferred Securities [Member] Securities	Jun. 30, 2013 Trust Preferred Securities [Member] Non-rated [Member]	Jun. 30, 2013 Single-issuer bank trust preferred securities [Member]	Dec. 31, 2012 Single-issuer bank trust preferred securities [Member]	Jun. 30, 2013 Perpetual Preferred Securities [Member] Security	Jun. 30, 2013 Pooled trust preferred securities [Member] Securities	Dec. 31, 2012 Pooled trust preferred securities [Member] Securities	Jun. 30, 2013 Pooled trust preferred securities [Member] Investment grade [Member] Securities	Jun. 30, 2013 Pooled trust preferred securities [Member] Non-investment grade [Member] Securities	Jun. 30, 2013 Residential mortgage-backed securities [Member]	Dec. 31, 2012 Residential mortgage-backed securities [Member]	Jun. 30, 2013 Residential mortgage-backed securities [Member] Investment grade [Member] Securities	Jun. 30, 2013 Private label mortgage-backed securities [Member]	Jun. 30, 2013 Private label mortgage-backed securities [Member] Non-investment grade [Member] Securities
Investment Securities [Line Items]
Held to maturity, fair value	$ 1,764,181,000		$ 1,764,181,000		$ 1,657,950,000															$ 963,575,000	$ 838,116,000
Available for sale	958,656,000		958,656,000		807,816,000	16,000,000										12,200,000				573,827,000	510,154,000
Fair value of trading securities	14,170,000		14,170,000		22,157,000								14,200,000	22,200,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	108		108		74						9				2	3	3	1	2					1
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	127		127		34							4
Fair value of investments held to maturity pledged as collateral	759,500,000		759,500,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years	5.0		5.0
Gross unrealized losses	43,474,000		43,474,000		19,479,000	469,000									1,600,000	4,300,000				20,812,000	3,359,000	18,400,000		1,600,000
Number of non-investment grade private label mortgage-backed securities																						25
Amortized Cost	986,105,000		986,105,000		813,474,000	16,500,000									10,000,000	16,500,000				590,225,000	506,695,000
Unrealized losses, available-for-sale securities	43,474,000		43,474,000		19,479,000													2,600,000		20,812,000	3,359,000
Fair value of securities available for sale pledged as collateral	421,900,000		421,900,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years	3.2		3.2
Other-than-temporarily impaired trust preferred securities, amortized cost	41,800,000
Other-than-temporarily impaired trust preferred securities, fair value	47,300,000		47,300,000
Impairment charge part of combined amortized cost of the securities							4,500,000	18,300,000
Net impairment losses on securities		550,000		550,000
Other-than-temporarily impaired mortgage-backed securities, amortized cost																							27,700,000
Other-than-temporarily impaired mortgage-backed securities, fair value																							28,300,000
Gains from sales transactions										3,400,000
Preferred stock, amortized cost									941,000
Interest income on trading securities	$ 413,000	$ 462,000	$ 855,000	$ 884,000