Accounts Payable and Accrued Liabilities (Schedule of Accounts Payable and Accrued Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accounts payable	$ 6,284	$ 4,008
Goods received not yet invoiced	4,358	5,574
Accrued property taxes	3,105	2,751
Workers' compensation	3,589	2,969
Other	7,567	5,813
Total accounts payable and accrued liabilities	$ 24,903	$ 21,115