Summary of Performance-based Award Activity (Detail) - Performance Shares - USD ($)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Number of shares
Beginning balance	[1]	66,150
Grants	[1]	82,000	66,650
Cancellations	[1]	(2,188)	(500)
Ending balance	[1]	145,962	66,150
Total unrecognized compensation expense remaining	[1]	$ 1,313,200
Weighted-average years expected to be recognized over	[1]	1 year 7 months 6 days
Weighted-average grant date fair value
Beginning balance		$ 14.84
Grants		15.69	$ 14.84
Cancellations		14.94	14.84
Ending balance		$ 15.32	$ 14.84

[1] Represents the target number of shares to be issued for each performance-based award.