Loans Receivable - Schedule of Carrying Amount of Acquired Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans Receivable [Line Items]
Acquired Impaired Loans	$ 190,837	$ 213,645
Acquired Performing Loans	813,336	879,111
Total Covered Loans	1,004,173	1,092,756
Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	18,388	20,232
Acquired Performing Loans	158,940	166,932
Total Covered Loans	177,328	187,164
Residential Mortgage Loans [Member] | Residential 1-4 Family [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	18,388	20,232
Acquired Performing Loans	158,940	166,932
Total Covered Loans	177,328	187,164
Commercial Loans [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	149,764	170,499
Acquired Performing Loans	504,889	557,395
Total Covered Loans	654,653	727,894
Commercial Loans [Member] | Real Estate [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	146,932	167,742
Acquired Performing Loans	420,689	473,101
Total Covered Loans	567,621	640,843
Commercial Loans [Member] | Business [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	2,832	2,757
Acquired Performing Loans	84,200	84,294
Total Covered Loans	87,032	87,051
Consumer And Other Loans [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	22,685	22,914
Acquired Performing Loans	149,507	154,784
Total Covered Loans	172,192	177,698
Consumer And Other Loans [Member] | Home Equity [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	21,917	22,094
Acquired Performing Loans	146,561	152,117
Total Covered Loans	168,478	174,211
Consumer And Other Loans [Member] | Other [Member]
Loans Receivable [Line Items]
Acquired Impaired Loans	768	820
Acquired Performing Loans	2,946	2,667
Total Covered Loans	$ 3,714	$ 3,487