Stock-Based Compensation - Summary of Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of shares
Number of shares, outstanding | shares	137,157
Number of shares, granted | shares	0
Number of shares, exercised | shares	(27,349)
Number of shares, forfeited | shares	0
Number of shares, outstanding | shares	109,808
Number of shares, vested and exercisable | shares	109,808
Weighted Average Exercise Price
Weighted average exercise price, outstanding (in $ per share) | $ / shares	$ 17.77
Weighted average exercise price, granted (in $ per share) | $ / shares	0.00
Weighted average exercise price, exercised (in $ per share) | $ / shares	23.12
Weighted average exercise price, forfeited (in $ per share) | $ / shares	0.00
Weighted average exercise price, outstanding (in $ per share) | $ / shares	16.44
Weighted average exercise price, vested and exercisable (in $ per share) | $ / shares	$ 16.44