Segment information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of operating segments | segment	1
Total sales outside of U.S.	$ 1,353,215	$ 1,359,132	$ 1,289,386
Property and equipment, net	243,717	245,201
Outside The United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total sales outside of U.S.	850,000	859,000	816,000
Property and equipment, net	$ 130,000	$ 132,000	$ 132,000