Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Net long-term deferred assets and (liabilities) relating to:
Accounts receivable and inventory reserves	$ 587	$ 351
Warranty accrual	3,165	3,405
Other accruals	1,715	1,248
Share-based compensation	1,784	1,099
Donations	463	691
Other, net	738	986
Total deferred income tax assets	8,452	7,780
Property & equipment	(17,983)	(16,486)
Total deferred income tax liabilities	(17,983)	(16,486)
Net deferred income tax liabilities	$ 9,531	$ 8,706