Accounting Policies - VIEs, Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Current assets	$ 33,066	$ 42,732
Non-current assets	6,466	26,346
Current liabilities	12,953	12,449
Non-current liabilities	8,780	$ 30,675
Bayou Perma-Pipe Canada, Ltd | Disposed of by Sale
Variable Interest Entity [Line Items]
Total assets held for sale	25,400
Total liabilities held for sale	$ 9,800