Stock-Based Compensation - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of shares, Beginning Balance | shares	483,021
Number of shares, Granted | shares	92,681
Number of shares, Settled | shares	(75,142)
Number of shares, Ending Balance | shares	500,560
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Beginning Balance (in $ per share) | $ / shares	$ 104.16
Weighted Average Grant Date Fair Value, Granted (in $ per share) | $ / shares	139.49
Weighted Average Grant Date Fair Value, Settled (in $ per share) | $ / shares	109.85
Weighted Average Grant Date Fair Value, Ending Balance (in $ per share) | $ / shares	$ 109.95