Acquisitions - Summary of Merger-Related Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Summary of merger-related expenses
Salaries and employee benefits	$ 356,551	$ 346,098
Equipment and net occupancy	65,159	65,043
Printing, postage and supplies	10,699	11,872
Other cost of operations	170,406	170,959
Bank Acquisition [Member]
Summary of merger-related expenses
Salaries and employee benefits	536	1,973
Equipment and net occupancy	201	15
Printing, postage and supplies	827
Other cost of operations	3,168	740
Total merger-related expenses	$ 4,732	$ 2,728