Stock-Based Compensation - Summary of Stock Option Activity (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning Balance, Shares | shares	122,547
Granted, Shares | shares	61,514
Ending Balance, Shares | shares	184,061
Options Exercisable, Shares | shares	51,079
Beginning Balance, Weighted Average Exercise Price | $ / shares	$ 57.74
Granted, Weighted Average Exercise Price | $ / shares	72.52
Ending Balance, Weighted Average Exercise Price | $ / shares	62.68
Options Exercisable, Weighted Average Exercise Price | $ / shares	$ 47.96
Ending Balance, Weighted Average Remaining Terms (years)	3 years 7 months 6 days
Options Exercisable, Weighted Average Remaining Terms (years)	2 years 8 months 12 days
Ending Balance, Aggregate Intrinsic Value | $	$ 1,875,799
Options Exercisable, Aggregate Intrinsic Value | $	$ 1,184,360