Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0	$ 0
Amortization of other intangible assets	2,232,000	2,201,000	$ 6,721,000	6,898,000
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