Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 428,234,000		$ 428,234,000		$ 428,234,000
Goodwill impairment			0	0
Net recoveries of impairment charges on its loan servicing rights	131,000	357,000	273,000	2,400,000
Total amortization expense - other intangible assets	2,200,000	2,300,000	6,900,000	5,800,000
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	$ 0	$ 0