Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Net long-term deferred assets and (liabilities) relating to:
Accounts receivable and inventory reserves	$ 835	$ 401
Warranty accrual	3,523	3,105
Other accruals	1,919	2,445
Share-based compensation	3,906	3,264
Donations	194	80
Other, net	2,140	851
Total deferred income tax assets	12,517	10,146
Property & equipment	(27,814)	(19,405)
Total deferred income tax liabilities	(27,814)	(19,405)
Net deferred income tax liabilities	$ 15,297	$ 9,259