Investments in Affiliates - Investments in Affiliates (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	$ 82,109	$ 84,354	$ 99,495
Joint Venture Unconsolidated [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	82,109	84,354	99,495
Joint Venture Unconsolidated [Member] | Foreign Affiliates [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	55,563	55,715	63,000
Joint Venture Unconsolidated [Member] | Real Estate [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	17,781	19,676	27,591
Joint Venture Unconsolidated [Member] | Asphalt Terminal [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	$ 8,765	$ 8,963	$ 8,904