Investments in Affiliates - Investments in Affiliates (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	$ 84,840	$ 38,469	$ 39,946
Joint Venture Unconsolidated [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	84,840	38,469	39,946
Joint Venture Unconsolidated [Member] | Foreign Affiliates [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	54,620	0	0
Joint Venture Unconsolidated [Member] | Equity Method investments in Real Estate Affiliates [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	20,930	29,472	28,634
Joint Venture Unconsolidated [Member] | Equity Method Investment in Asphalt Terminal Affiliate [Member]
Investments In And Advances To Affiliates [Line Items]
Investments in affiliates	$ 9,290	$ 8,997	$ 11,312