Supplemental balance sheet and cash flow information (other non-current assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other non-current assets
Contract acquisition costs	$ 63,895	$ 65,792	$ 58,792	$ 74,101
Loans and notes receivable from Safeguard distributors	44,276	21,313
Postretirement benefit plan asset (Note 12)	39,849	23,940
Deferred advertising costs	6,135	7,309
Other	5,601	6,708
Other non-current assets	$ 159,756	$ 125,062