Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Net long-term deferred assets and (liabilities) relating to:
Accounts receivable and inventory reserves	$ 1,052	$ 835
Warranty accrual	3,776	3,523
Other accruals	747	1,919
Share-based compensation	4,102	3,906
Donations	297	194
Other, net	2,457	2,140
Total deferred income tax assets	12,431	12,517
Property & equipment	(40,755)	(27,814)
Total deferred income tax liabilities	(40,755)	(27,814)
Net deferred income tax liabilities	$ 28,324	$ 15,297