Accounts Payable and Accrued Liabilities (Schedule of Accounts Payable and Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Payable and Accrued Liabilities [Abstract]
Accounts payable	$ 5,844	$ 4,008
Goods received not yet invoiced	6,095	5,574
Accrued property taxes	2,763	2,751
Accrued payroll	1,825	1,403
Workers' compensation reserve	3,670	2,969
Group health insurance	2,200	1,332
Other	4,024	3,078
Total accounts payable and accrued liabilities	$ 26,421	$ 21,115