Cash flow information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest, net of amount capitalized and AFUDC - borrowed of $914, $9,288 and $10,069 in 2016, 2015 and 2014, respectively	$ 87,920	$ 88,775	$ 81,195
Income taxes paid, net	105,908	61,405	80,090
Property, plant and equipment additions in accounts payable	22,712	39,754	12,791
Capitalized interest and AFUDC borrowed	914	9,288	10,069
Continuing and discontinued operations [Member]
Income taxes paid, net	$ 1,300	$ 2,400	$ 69,800