New accounting standards ASU 2014-09 (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other accrued liabilities	$ 204,328		$ 186,010	$ 188,373
Deferred income taxes	346,218		347,271	666,905
Other	1,181,919		1,179,140	890,107
Retained earnings	$ 1,051,469		1,040,748	$ 911,702
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other accrued liabilities		$ 186,913
Deferred income taxes		346,939
Other		1,179,539
Retained earnings		1,039,778
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other accrued liabilities			186,010
Deferred income taxes			347,271
Other			1,179,140
Retained earnings			$ 1,040,748
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other accrued liabilities		903
Deferred income taxes		(332)
Other		399
Retained earnings		$ (970)