Accounts Payable and Accrued Liabilities (Schedule of Accounts Payable and Accrued Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Abstract]
Accounts payable	$ 7,079	$ 5,844
Goods received not yet invoiced	6,982	6,095
Accrued property taxes	3,149	2,763
Accrued payroll	2,345	1,825
Workers' compensation reserve	3,872	3,670
Group health insurance	2,400	2,200
Other	3,700	4,024
Total accounts payable and accrued liabilities	$ 29,527	$ 26,421