Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 428,234,000		$ 428,234,000		$ 428,234,000
Goodwill, Other Changes			0	0
Net recoveries of impairment charges on its loan servicing rights	759,000	401,000	2,100,000	19,000
Impairment of core deposits and intangibles	0	0	0	0
Total amortization expense - other intangible assets	$ 1,900,000	$ 2,500,000	$ 3,500,000	$ 4,500,000
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			17 years