Earnings Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted earnings per share excludes antidilutive effect (in shares)	100,000	100,000	0
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted earnings per share excludes antidilutive effect (in shares)	100,000	400,000	1,400,000
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Diluted earnings per share excludes antidilutive effect (in shares)	300,000	200,000	200,000