The principal activity from which the Company generates its revenue is the manufacturing of production parts for automotive OEMs and automotive suppliers, as well as the sale of medical products and equipment primarily through distributor and group purchasing organization agreements.

We record a receivable when revenue is recognized at the time of invoicing and unearned revenue when revenue is recognized subsequent to invoicing. For contracts where control of the goods or service is transferred to the customer over time, or whose terms required the customer to make milestone payments throughout the fulfillment period, the timing of revenue recognition is likely to differ from the timing of invoicing to customers.

Most of Gentherm’s unearned revenue pertains to LTAs containing a material right. In the early periods of an LTA containing a material right, when payments collected from the customer are greater than the standalone selling price of the production parts, revenue associated with the material right is deferred. In future periods, when amounts collected from customers as payment is less than the standalone selling price of the production parts delivered, the deferred revenue is reversed into revenue. For LTAs containing a material right and, thus, the timing of revenue recognition is likely to differ from the timing of invoicing to customer, the aggregate amount of transaction price allocated to material rights that remained unsatisfied under LTAs as of December 31, 2019 was $579. We expect to recognize into revenue, 69% of this balance in 2020, and the remaining 11%, 11% and 9% in 2021, 2022 and 2023, respectively.

	December 31, 2019		December 31, 2018
Automotive	$	579	$	1,597
Industrial		—		—
Total	$	579	$	1,597

Changes in unearned revenue for the year ended December 31, 2019 were as follows:

Balance, beginning of period	$	1,597
Additions to unearned revenue		234
Reclassified to revenue		(1,238	)
Currency impacts		(14	)
Balance, end of period	$	579

Revenue allocated to remaining performance obligations represent contracted revenue that has not yet been recognized, which includes unearned revenue and amounts that will be invoiced and recognized as revenue in future periods.