Selected Quarterly Data (unaudited) - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effect of Fourth Quarter Events [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$ 13,300,000				$ 0
Mark-to-market actuarial gains (losses) on pension and post-retirement benefit plans	$ 4,200,000
Disposal Group, Including Discontinued Operation, Other Expense		$ 0	$ 0	$ 554,700,000