Significant acquisitions - Assets Acquired Liabilities Assumed (Details) - USD ($) $ in Thousands		6 Months Ended
	May 26, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Consideration:
Total purchase price		$ 68,632	$ 0
Assets acquired and liabilities assumed:
Goodwill		$ 123,023		$ 113,343
Cap Juluca
Consideration:
Agreed cash consideration	$ 70,759
Less: Working capital adjustment	(2,107)
Total purchase price	68,652
Assets acquired and liabilities assumed:
Cash and cash equivalents	20
Accounts receivable	112
Prepaid expenses and other	45
Inventories	108
Property, plant and equipment	59,159
Other intangible assets	6,100
Accounts payable	(595)
Accrued liabilities	(360)
Deferred revenue	(1,437)
Goodwill	5,500
Net assets acquired	$ 68,652