Supplemental Data - Supplemental Cash Flow Data (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Disclosure of Cash Flow Information
Cash paid during the year for interest, net of interest expense capitalized	$ 11.3	$ 10.0	$ 10.6
Cash paid during the year for income taxes, net of refunds	7.6	15.0	16.2
Non-cash investing activities:
Liability for equipment acquired	5.4	11.1	6.6
Net cash provided by (used in) changes in working capital
Accounts receivable	(10.2)	1.5	(5.2)
Inventories	(11.7)	4.3	7.7
Income taxes receivable/payable	4.5	(1.5)	1.0
Prepaid and other current assets	(0.4)	0.0	(4.8)
Accounts payable	10.6	(2.7)	(0.5)
Accrued expenses	(4.2)	(2.8)	3.2
Other	(0.4)	0.0	0.4
Total	$ (11.8)	$ (1.2)	$ 1.8