Goodwill and Other Intangible Assets - Activity in Valuation Allowance for Mortgage Servicing Rights (Detail) (Mortgage Servicing Rights [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Mortgage Servicing Rights [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance, beginning of period	$ (250)	$ (497)	$ (793)
Additions	0	0	0
Reductions	250	247	296
Direct write-downs	0	0	0
Valuation allowance, end of period	$ 0	$ (250)	$ (497)