Equity - Accumulated other comprehensive income (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2016	$ (73,914)
Currency translation adjustment, net of income tax expense of $9,116	14,956
Changes related to benefit plans, net of income tax expense of $11	29
Balance at June 30, 2017	(58,929)
Currency Translation [Member]
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2016	(71,425)
Currency translation adjustment, net of income tax expense of $9,116	14,956
Changes related to benefit plans, net of income tax expense of $11	0
Balance at June 30, 2017	(56,469)
Employee Benefit Plans [Member]
Components of Accumulated Other Comprehensive Loss
Balance at December 31, 2016	(2,489)
Currency translation adjustment, net of income tax expense of $9,116	0
Changes related to benefit plans, net of income tax expense of $11	29
Balance at June 30, 2017	$ (2,460)