Business Combinations - Additional Information (Detail)		3 Months Ended		6 Months Ended
	Feb. 29, 2016 USD ($) Branch	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 01, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition date				Oct. 16, 2009
Goodwill		$ 88,174,000		$ 88,174,000			$ 74,244,000
Non-recurring merger related expenses		355,000	$ 0	$ 1,204,000	$ 0
County Commerce Bank [Member]
Business Acquisition [Line Items]
Acquisition date				Feb. 29, 2016
Number of branches owned by merger company | Branch	4
Acquired assets and assumed liabilities, cash	$ 20,600,000
Assets and assumed all of the liabilities, stock	21,600,000
Goodwill						$ 13,900,000
Total fair value of assets acquired	252,400,000
Cash and balances due from depository institutions	54,800,000
FHLB stock	1,500,000
Loans and lease finance receivables	168,000,000
Fixed assets	8,600,000
Core deposit intangible assets	3,900,000
Other assets	1,700,000
Total fair value of liabilities assumed	230,800,000
Deposits	224,200,000
Other liabilities	1,600,000
FHLB advances	$ 5,000,000
Non-recurring merger related expenses		$ 355,000		$ 1,200,000