Segment Information and Foreign Operations - Product Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue by product type
Revenue	$ 33,735	$ 22,134	$ 65,085	$ 42,857
Substrates
Revenue by product type
Revenue	24,905	16,874	48,278	33,755
Raw materials and others
Revenue by product type
Revenue	$ 8,830	$ 5,260	$ 16,807	$ 9,102

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details