Stock-Based Compensation - Summary of Stock-Based Compensation Grants (Detail)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Time Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted | shares	87,154
Weighted-Average Grant Price Per Share | $ / shares	$ 54.69
Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted | shares	80,570
Weighted-Average Grant Price Per Share | $ / shares	$ 35.26
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Awards Granted | shares	21,260
Weighted-Average Grant Price Per Share | $ / shares	$ 56.21