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
Business Acquisition [Line Items]
Salaries and employee benefits	$ 66,888	$ 64,524	$ 129,922	$ 122,482
Net occupancy and equipment	11,154	11,725	22,369	22,536
Merger [Member]
Business Acquisition [Line Items]
Salaries and employee benefits		1,705		3,055
Consulting		194		4,209
Legal		728		1,498
Branch writeoffs		0		1,371
Net occupancy and equipment		31		2,840
All other		660		1,824
Total merger-related expenses		3,318		14,797
Merger [Member] | Tower [Member]
Business Acquisition [Line Items]
Salaries and employee benefits		1,705		3,055
Consulting		194		4,143
Legal		586		1,319
Branch writeoffs		0		1,371
Net occupancy and equipment		31		2,840
All other		25		1,189
Total merger-related expenses		2,541		13,917
Merger [Member] | Abington [Member]
Business Acquisition [Line Items]
Salaries and employee benefits		0		0
Consulting		0		66
Legal		142		179
Branch writeoffs		0		0
Net occupancy and equipment		0		0
All other		635		635
Total merger-related expenses		$ 777		$ 880