Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	9 Months Ended
	Aug. 23, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Line Items]
Reserves for environmental remediation liabilities		$ 16.0	$ 16.0	$ 16.0	$ 16.0
Accounts payable and accrued liabilities of environmental remediation reserves		4.3	4.3	4.3	4.3
Asset retirement obligations		5.2	5.2	5.2	5.0
Asset Retirement Obligation, current		0.7	0.7	0.7	0.9
Asset Retirement Obligation, non-current		4.5	4.5	$ 4.5	$ 4.1
Mr. Craig T. Bouchard
Commitments And Contingencies Disclosure [Line Items]
Description of postemployment severance				In connection with his separation, Mr. Bouchard received $2.0 million of cash severance, $0.5 million of which was paid in September 2016, with the remaining $1.5 million to be paid beginning October 31, 2016 through August 31, 2018. Additionally, certain of Mr. Bouchard’s equity awards were forfeited, while others were modified with no further service requirement. As a result, in the three months ending September 30, 2016, the Company recognized $1.5 million of share-based compensation expense related to the awards that continue to vest.
Postemployment severance cost	$ 2.0
Postemployment severance payment		0.5
Postemployment severance cost to be paid beginning October 31, 2016 through August 31, 2018		$ 1.5	1.5	$ 1.5
Share-based compensation expense			$ 1.5