Mortgage Banking Activities - Key Economic Assumptions in Measuring Value of Mortgage Servicing Rights (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Mortgage Banking [Abstract]
Weighted average prepayment rate	229	401
Weighted average life (in years)	4 years	3 years 11 months 5 days
Weighted average discount rate	8.00%	8.00%