Business Combinations - Additional Information (Detail)			3 Months Ended		9 Months Ended
	Mar. 10, 2017 USD ($) Branch	Feb. 29, 2016 USD ($) Branch	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Acquisition date					Oct. 16, 2009
Goodwill			$ 116,564,000	$ 88,174,000	$ 116,564,000	$ 88,174,000	$ 89,533,000
Non-recurring merger related expenses			250,000	353,000	$ 2,176,000	1,557,000
Valley Commerce Bancorp [Member]
Business Acquisition [Line Items]
Acquisition date					Mar. 10, 2017
Acquired assets and assumed liabilities for cash	$ 23,200,000
Assets and assumed all of the liabilities, stock	37,600,000
Goodwill	27,000,000
Total fair value of assets acquired	405,900,000
Cash and cash equivalents	28,300,000
FHLB stock	2,000,000
Loans and lease finance receivables	309,700,000
Fixed assets	5,300,000
Bank-Owned Life Insurance	9,400,000
Core deposit intangible assets	3,200,000
Other assets	21,000,000
Total fair value of liabilities assumed	368,300,000
Deposits	361,800,000
Other liabilities	$ 6,500,000
Non-recurring merger related expenses			$ 250,000		$ 2,200,000
Valley Business Bank [Member]
Business Acquisition [Line Items]
Number of branches owned by merger company | Branch	4
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 for cash		$ 20,600,000
Assets and assumed all of the liabilities, stock		21,600,000
Goodwill		15,300,000
Total fair value of assets acquired		252,400,000
Cash and cash equivalents		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		289,000
Total fair value of liabilities assumed		230,800,000
Deposits		224,200,000
Other liabilities		1,600,000
Non-recurring merger related expenses				$ 145,000		$ 1,300,000
FHLB advances		$ 5,000,000