Accounts Payable and Accrued Liabilities (Schedule of Accounts Payable and Accrued Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accounts payable	$ 5,215	$ 4,008
Goods received not yet invoiced	5,114	5,574
Accrued property taxes	3,170	2,751
Workers' compensation	4,541	2,969
Other	8,631	5,813
Total accounts payable and accrued liabilities	$ 26,671	$ 21,115