Share-Based Compensation - Summary of Number of Awards Granted and Grand Date Fair Value (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets Valuation Allowance [Line Items]
Grant Date Fair Value	$ 24.20
TSR Awards [Member]
Deferred Tax Assets Valuation Allowance [Line Items]
Number of awards granted in fair values, Shares	46	101	36
Grant Date Fair Value	$ 29.84	$ 9.38	$ 28.61
ROIC Awards [Member]
Deferred Tax Assets Valuation Allowance [Line Items]
Number of awards granted in fair values, Shares	53	101	36
Grant Date Fair Value	$ 24.20	$ 11.31	$ 25.16