Mortgage Servicing Rights - Changes in mortgage servicing rights balance (Detail) (Mortgage servicing rights [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Mortgage servicing rights [Member]
Servicing Asset at Amortized Cost [Line Items]
Beginning of period	$ 4,723	$ 3,067	$ 4,152	$ 2,739
Servicing rights capitalized	871	609	1,639	1,036
Amortization of servicing rights	(381)	(373)	(812)	(684)
Changes in valuation allowance	14	(27)	248	185
End of period	5,227	3,276	5,227	3,276
Mortgage loans serviced for others	$ 705,999	$ 491,536	$ 705,999	$ 491,536