Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Random sample percentage of securities for each quarter	100.00%
Credit loss recognized	$ 0	$ 0	$ 0
Total gains or losses included in earnings	(589,000)	(111,000)
Interest rate swaps transferred into Level 3 from Level 2	536,000	0
Corporate securities transferred from Level 3 to Level 2	(536,000)	0
Impaired loans considered to be credit risk of non-collection	100,000
Updated appraisal requirement floor	250,000
Other real estate owned	6,805,000	9,398,000
Financial instrument of credit risk	165,000	200,000
Provision for credit losses	18,480,000	14,948,000	$ 11,196,000
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total gains or losses included in earnings	0	0
Interest rate swaps transferred into Level 3 from Level 2	536,000	0
Corporate securities transferred from Level 3 to Level 2	$ 0	$ 0