Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Net long-term deferred assets and (liabilities) relating to:
Accounts receivable and inventory reserves	$ 351	$ 355
Warranty accrual	3,405	3,263
Other accruals	1,248	1,238
Share-based compensation	1,099	707
Donations	691	1,309
Other, net	986	888
Total deferred income tax assets	7,780	7,760
Property & equipment	(16,486)	(15,294)
Total deferred income tax liabilities	(16,486)	(15,294)
Net deferred income tax liabilities	$ 8,706	$ 7,534