Stock-Based Compensation - Summary of Stock-Based Compensation Grants (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Time Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted	36,105
Weighted-Average Grant Price Per Share	$ 72.50
Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted	43,307
Weighted-Average Grant Price Per Share	$ 57.54
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted	18,739	0
Weighted-Average Grant Price Per Share	$ 70.75