Accounts Receivable Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 428,785	$ 375,993
Allowance for doubtful accounts	(12,983)	(12,070)
Accounts receivable, net	415,802	363,923
Accounts receivable - trade [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	407,305	353,347
Accounts receivable - grants from outside parties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	12,178	10,652	$ 10,800
Accounts receivable - insurance and other third-party claims [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	9,302	$ 11,994
Pentalver Transport Limited [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net	$ 27,300