Equity - Accumulated other comprehensive income (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2017	$ (53,801)
Currency translation adjustment, net of income tax benefit of $2,950	(9,137)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	27,305
Changes related to benefit plans, net of income tax expense of $1	3
Balance at March 31, 2018	(35,630)
Currency Translation [Member]
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2017	(51,014)
Currency translation adjustment, net of income tax benefit of $2,950	(9,137)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	27,305
Changes related to benefit plans, net of income tax expense of $1	0
Balance at March 31, 2018	(32,846)
Employee Benefit Plans [Member]
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2017	(2,787)
Currency translation adjustment, net of income tax benefit of $2,950	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0
Changes related to benefit plans, net of income tax expense of $1	3
Balance at March 31, 2018	$ (2,784)