Divestitures and discontinued operations - (Long-Lived Assets Held-for-Sale) (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long lived assets held-for-sale fair value disclosure	$ 14,264	$ 15,779
Terminalling and storage
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long lived assets held-for-sale fair value disclosure	10,637	10,852
Marine transportation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long lived assets held-for-sale fair value disclosure	$ 3,627	$ 4,927