Shared-Based Compensation - Summary of Number of Awards Granted and Grand Date Fair Value (Detail) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value	$ 24.55
TSR Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards granted in fair values, Shares | shares	55
Grant Date Fair Value	$ 24.65
ROIC Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards granted in fair values, Shares | shares	55
Grant Date Fair Value	$ 24.55