Residential Mortgage-Banking Activities - Summary of Changes in Residential Mortgage Servicing Rights (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compliance with Regulatory Capital Requirements for Mortgage Companies [Line Items]
Mortgage-servicing rights portfolio, net of valuation allowance, beginning of period	$ 2,586	$ 2,896	$ 3,039
Capitalized mortgage-servicing rights	864	465	655
Mortgage-servicing rights portfolio amortization and impairment	(866)	(775)	(798)
Mortgage-servicing rights portfolio, net of valuation allowance, end of period	$ 2,584	$ 2,586	$ 2,896