Supplemental Cash Flow Information - Reconciliation of Total Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Information
Cash and cash equivalents	$ 24.9	$ 27.2	$ 35.7
Cash and cash equivalents-discontinued operations			0.1
Restricted cash and restricted cash equivalents	0.7	1.0
Cash, cash equivalents, restricted cash and restricted cash equivalents, end of period	32.8	32.7	43.3	$ 65.7
Prepaid Expenses, Supplies, and Other Current Assets
Supplemental Cash Flow Information
Restricted cash and restricted cash equivalents	0.7	1.0	3.9
Other Noncurrent Assets
Supplemental Cash Flow Information
Restricted cash and restricted cash equivalents	$ 7.2	$ 4.5	$ 3.6