Goodwill and Other Intangible Assets - Schedule of Mortgage Servicing Rights at Carrying Values (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 78,968	$ 57,665
Accumulated Amortization	(38,851)	(37,304)
Net Carrying Amount	40,117	20,361
Mortgage Servicing Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,988	4,751
Accumulated Amortization	(1,453)	(1,253)
Net Carrying Amount	$ 3,535	$ 3,498