Reclassifications out of accumulated other comprehensive (loss) (Details 10) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (84,614)	$ (82,788)	$ (87,848)
Income taxes	(47,485)	(65,041)	(93,132)
Other income	(238)	8,767	5,167
Net income (loss)	272,318	281,203	$ (67,258)
Reclassification out of accumulated other comprehensive income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(2,715)	(1,499)
Reclassification adjustment for loss on derivative instruments included in net income (loss): | Reclassification out of accumulated other comprehensive income | Interest rate contract
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(591)	(590)
Income taxes	429	224
Net income (loss)	(162)	(366)
Amortization of postretirement liability losses included in net periodic benefit cost (credit) | Reclassification out of accumulated other comprehensive income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	721	645
Other income	(2,894)	(1,658)
Net income (loss)	(2,173)	(1,013)
Reclassification adjustment for loss on foreign currency translation adjustment included in net income (loss) | Reclassification out of accumulated other comprehensive income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	75	0
Other income	(324)	0
Net income (loss)	(249)	0
Reclassification adjustment for loss on available-for-sale investments included in net income (loss) | Reclassification out of accumulated other comprehensive income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	35	65
Other income	(166)	(185)
Net income (loss)	$ (131)	$ (120)