Summary of Estimated Future Expense from Amortization of CDI and MSRs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Expected Amortization Expense [Line Items]
2012	$ 20,047
2013	15,945
2014	8,330
2015	5,344
2016	2,390
2017 and thereafter	208
Total remaining intangible assets	52,264
Core deposit intangibles
Expected Amortization Expense [Line Items]
2012	19,644
2013	15,784
2014	8,298
2015	5,344
2016	2,390
2017 and thereafter	208
Total remaining intangible assets	51,668
Mortgage Servicing Rights
Expected Amortization Expense [Line Items]
2012	403
2013	161
2014	32
Total remaining intangible assets	$ 596