Quarterly report pursuant to Section 13 or 15(d)

Revenue (Notes)

Revenue (Notes)
6 Months Ended
Jun. 30, 2019
Revenue from Contract with Customer [Abstract]  
Revenue Revenue
Unbilled accounts receivable (“AR”) for the periods presented primarily represent the difference between revenue recognized based on the relative selling price of the related performance obligations and the contractual billing terms in the arrangements. Deferred revenue for the periods presented primarily relates to extended service contracts, installation, and training, for which the service fees are billed in advance. The associated deferred revenue is generally recognized ratably over the extended service period or when installation and training are complete.

The following table summarizes the changes in the unbilled AR and deferred revenue balances for the six months ended June 30, 2019 (in thousands):
Unbilled AR, December 31, 2018


Transferred to Trade Receivable
Unbilled AR, June 30, 2019

Deferred Revenue, December 31, 2018


Revenue Recognized
Deferred Revenue, June 30, 2019

At June 30, 2019, the short-term portion of deferred revenue of $19.9 million and the long-term portion of $4.3 million were included in deferred revenue and other long-term liabilities respectively, in the consolidated balance sheet. As of June 30, 2019, the Company expects to recognize revenue associated with deferred revenue of
approximately $12.8 million in 2019, $8.3 million in 2020, $1.5 million in 2021, $0.9 million in 2022, and $0.7 million thereafter.