Acquisitions (Summary of Merger-Related Expenses) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Business Acquisition [Line Items]
Salaries and employee benefits	$ 62,236	$ 53,315	$ 184,718	$ 157,719
Net occupancy and equipment	11,350	8,982	33,886	27,499
Abington [Member]
Business Acquisition [Line Items]
Salaries and employee benefits	2	0	2	0
Consulting	2	607	68	628
Legal	193	602	372	1,983
Branch writeoffs	0	0	0	0
Net occupancy and equipment	0	0	0	0
All other	170	84	805	169
Merger-related expenses	367	1,293	1,247	2,780
Tower [Member]
Business Acquisition [Line Items]
Salaries and employee benefits	489	0	3,544	0
Consulting	403	0	4,546	0
Legal	152	0	1,471	0
Branch writeoffs	0	0	1,371	0
Net occupancy and equipment	0	0	2,840	0
All other	89	0	1,278	0
Merger-related expenses	1,133	0	15,050	0
Merger [Member]
Business Acquisition [Line Items]
Salaries and employee benefits	491	0	3,546	0
Consulting	405	607	4,614	628
Legal	345	602	1,843	1,983
Branch writeoffs	0	0	1,371	0
Net occupancy and equipment	0	0	2,840	0
All other	259	84	2,083	169
Merger-related expenses	$ 1,500	$ 1,293	$ 16,297	$ 2,780