3.          REVENUE

Adoption of ASC 606, “Revenue from Contracts with Customers”. On January 1, 2018, the Company adopted ASC 606 using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance with our historic accounting under ASC 605.

There was no material impact on the Company’s financial statements as a result of adopting ASC 606 for the twelve months ended December 31, 2018.

The following tables present our revenues disaggregated by revenue source (in thousands, unaudited).

Sales and usage-based taxes are excluded from revenues. No sales to an individual customer or in a country other than the United States accounted for more than 10% of the sales for the periods listed on the following table. Revenue, classified by the major geographic areas in which our customers are located, was as follows:

Revenue from external customers, classified by significant product and service offerings, was as follows:

Deferred revenue recognized for the year ended December 31, 2019 and 2018 was $165.0 million and $156.6 million, respectively. Changes in unearned revenue were as follows:

Revenue allocated to remaining performance obligations represents contracted revenue that has not yet been recognized (“contracted not recognized revenue”), which includes both unearned revenue and revenue that will be billed and recognized in future periods. The Company has no material contracted not recognized revenue as of December 31, 2019 or December 31, 2018.

At December 31, 2019 and December 31, 2018, the Company had long-term unearned revenue of $13.7 million and $11.1 million, respectively. Unearned short-term revenue is recognized over the next 12-month period. The majority of unearned long-term revenue is recognized over a period of five years or less with immaterial amounts recognized through 2025.