Merger Related Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Business Acquisition, Contingent Consideration [Line Items]
Salaries and employee benefits	$ 15,927	$ 14,676	$ 31,628	$ 29,300
Outside data services	1,828	999	3,107	1,994
Miscellaneous expenses	5,221	4,338	9,280	8,506
Total merger expenses			2,572
Acquisition-related Costs
Business Acquisition, Contingent Consideration [Line Items]
Salaries and employee benefits			737
Outside data services			1,031
Professional fees (legal, consulting, etc.)			683
Miscellaneous expenses			$ 121