Supplemental balance sheet and cash flow information (other non-current assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other non-current assets
Contract acquisition costs	$ 65,792	$ 58,792	$ 74,101	$ 35,421
Postretirement benefit plan asset (Note 12)	23,940	16,250
Loans and notes receivable from distributors	21,313	23,957
Deferred advertising costs	7,309	7,500
Other	6,708	7,313
Other non-current assets	$ 125,062	$ 113,812