Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0	$ 0
Total amortization expense - other intangible assets	2,100,000	2,300,000	$ 4,500,000	4,700,000
Core Deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years			11 years
Other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years			19 years
Core Deposits and Other
Finite-Lived Intangible Assets [Line Items]
Impairment of core deposits and intangibles	$ 0	$ 0	$ 0	$ 0