Acquisitions - Summary of Merger-Related Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Summary of merger-related expenses
Salaries and employee benefits	$ 323,136	$ 323,686	$ 679,687	$ 669,784
Equipment and net occupancy	64,278	65,376	129,437	130,419
Printing, postage and supplies	10,298	11,368	20,997	23,240
Other costs of operations	170,682	186,093	341,088	357,052
Bank Acquisition [Member]
Summary of merger-related expenses
Salaries and employee benefits	300	3,024	836	4,997
Equipment and net occupancy	489		690	15
Printing, postage and supplies	998		1,825
Other costs of operations	5,845	4,127	9,013	4,867
Total merger-related expenses	$ 7,632	$ 7,151	$ 12,364	$ 9,879