Mortgage Banking Activities - Key Economic Assumptions in Measuring Value of Mortgage Servicing Rights (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Mortgage Banking [Abstract]
Weighted average prepayment rate	232	401
Weighted average life (in years)	3 years 11 months 27 days	3 years 11 months 5 days
Weighted average discount rate	8.00%	8.00%