Property, plant, equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Land, buildings and leasehold improvements	$ 207,927	$ 188,679
Machinery and equipment	384,710	319,471
Computer equipment and software	122,890	108,547
Construction in progress	73,920	47,428
Property, plant and equipment, gross	789,447	664,125
Less: Accumulated depreciation	(406,448)	(361,226)
Property, plant and equipment, net	$ 382,999	$ 302,899	$ 316,123