Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 428,234,000		$ 428,234,000
Goodwill impairment	0	0
Net recoveries of impairment charges on its loan servicing rights	100,000	1,300,000
Total amortization expense - other intangible assets	2,400,000	1,600,000
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	11 years
Other [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	18 years
Core Deposits and Other [Member]
Finite-Lived Intangible Assets [Line Items]
Impairment of core deposits and intangibles	$ 0	$ 0