Details of Selected Balance Sheet Accounts - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Details of Selected Balance Sheet Accounts [Abstract]
Accrued compensation	$ 25,794	$ 23,131
Insurance liabilities	6,831	8,099
Accrued taxes, other than income taxes	3,591	2,461
Accrued leasehold restoration liability	838	766
Accrued product warranty reserves	654	1,113
Accrued commissions	1,335	1,305
Accrued claims	1,320	1,578
Other	5,526	6,880
Accrued Liabilities	$ 45,889	$ 45,333