Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 810,332
Intangible assets recognized or adjusted during the period			3,175
Currency translation during the period			74,817
Intangible assets subject to amortization, ending balance	$ 888,324		888,324
Accumulated amortization, beginning balance			555,873
Amortization during the period	7,421	$ 10,381	26,802	$ 29,439
Currency translation during the period			53,419
Accumulated amortization, ending balance	636,094		636,094
Intangible assets subject to amortization, net	252,230		252,230		$ 254,459
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			569,980
Intangible assets recognized or adjusted during the period			3,175
Currency translation during the period			45,597
Intangible assets subject to amortization, ending balance	618,752		618,752
Accumulated amortization, beginning balance			334,276
Amortization during the period			19,710
Currency translation during the period			25,689
Accumulated amortization, ending balance	379,675		379,675
Intangible assets subject to amortization, net	239,077		239,077
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			234,022
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			28,778
Intangible assets subject to amortization, ending balance	262,800		262,800
Accumulated amortization, beginning balance			220,598
Amortization during the period			6,970
Currency translation during the period			27,706
Accumulated amortization, ending balance	255,274		255,274
Intangible assets subject to amortization, net	7,526		7,526
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			6,330
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			442
Intangible assets subject to amortization, ending balance	6,772		6,772
Accumulated amortization, beginning balance			999
Amortization during the period			122
Currency translation during the period			24
Accumulated amortization, ending balance	1,145		1,145
Intangible assets subject to amortization, net	$ 5,627		$ 5,627