Transactions with WestRock and related-parties - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	May 15, 2016
Related Party Transaction
Accounts payable	$ 79.2		$ 83.1
WestRock
Related Party Transaction
Accounts payable				$ 16.5
WestRock | Minimum
Related Party Transaction
Percentage of long-term supply of CTO			45.00%
WestRock | Maximum
Related Party Transaction
Percentage of long-term supply of CTO			55.00%
WestRock | Purchase of Raw Material
Related Party Transaction
Purchases from related party	$ 20.1	$ 35.3