Stock-Based Compensation - Summary of Company's Non-Vested Options Under Company's Option Plans (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of Shares
Granted	0
Non-vested Options
Number of Shares
Balance at beginning of period	10,501
Granted	0
Vested	(10,501)
Balance at end of period	0
Weighted- Average Grant-date Fair Value
Balance at beginning of period | $ / shares	$ 3.31
Granted | $ / shares	0.00
Vested | $ / shares	3.31
Balance of end of period | $ / shares	$ 0.00