Supplemental cash flow information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash paid during the period for:
Interest	$ 40,930	$ 27,828	$ 30,147
Income taxes, net of refunds	19,804	18,306	$ 21,454
Decrease in accounts payable related to acquisition of property, plant, and equipment	$ 223	$ 229