Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Specific adjustments to impaired loans recognized	$ (7,000)	$ (143,000)	$ (165,000)
Transfers between level 1, 2 and 3		0
Liabilities measured at fair value on a recurring or nonrecurring basis	0	0
Transfers between level 1, 2 and 3			0
Liabilities measured at fair value on a recurring or nonrecurring basis			$ 0
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of Level 3 securities	180,315,000	180,315,000		$ 148,012,000
Unrealized loss	$ 404,000	$ 404,000		$ 876,000