Goodwill and Other Intangible Assets - Changes in 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]
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Beginning of period	$ 5,519	$ 4,152	$ 2,739
Servicing rights capitalized	1,118	2,485	2,727
Amortization of servicing rights	(1,378)	(1,365)	(1,610)
Changes in valuation allowance	250	247	296
End of period	5,509	5,519	4,152
Mortgage loans serviced for others	$ 796,835	$ 751,891	$ 604,801