Legal settlements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Legal Settlements [Abstract]
Legal settlements, including amounts awarded in a dispute and charges/amounts paid out in a separate dispute.	$ 0	$ 0	$ 1,798
Legal settlement charge			6,500
LegalSettlementChargeForLegalFees			700
Payments for Legal Settlements			7,500
Gross legal settlement award			8,800
Legal settlements			$ 5,300