The Company derives revenue primarily from the sale of MRIdian systems and related services as well as support and maintenance services on sold systems. Revenue is categorized as product revenue, service revenue and distribution rights revenue.

The following table presents revenue disaggregated by type and geography (in thousands):

	Years Ended December 31,
U.S.	2019		2018		2017
Product	$	41,985	$	32,265	$	9,529
Service		4,251		1,966		1,977
Total U.S. revenue	$	46,236	$	34,231	$	11,506

Outside of U.S. ("OUS")
Product	$	37,519	$	44,361	$	20,929
Service		3,552		1,895		1,132
Distribution rights		475		475		475
Total OUS revenue	$	41,546	$	46,731	$	22,536

Total
Product	$	79,504	$	76,626	$	30,458
Service		7,803		3,861		3,109
Distribution rights		475		475		475
Total revenue	$	87,782	$	80,962	$	34,042

The Company frequently enters into sales arrangements that include multiple performance obligations. Such performance obligations mainly consist of (i) sale of MRIdian systems, which generally includes installation and embedded software, and (ii) product support, which includes extended service and maintenance. For such arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price. The standalone selling price, or SSP, is determined based on observable prices at which the Company separately sells the products and services. If a SSP is not directly observable, the Company will estimate the SSP considering market conditions or internally approved pricing guidelines related to the performance obligations.

Product revenue is derived primarily from the sales of MRIdian system. The system contains both software and non-software components that together deliver essential functionality.

Certain revenue contracts have terms that result in the control of the system transferring to the customer upon delivery and inspection, as opposed to historically upon customer acceptance. For contracts in which control of the system transfers upon delivery and inspection, the Company recognizes revenue for the systems at the point in time when delivery and inspection by the customer has occurred. For these same contracts, the Company recognizes installation revenue over the period of installation as the installation services are performed and control is transferred to the customer. For all contracts in which control continues to transfer upon post-implementation customer acceptance, revenue for the system and installation will continue to be recognized upon customer acceptance.

Certain customer contracts with distributors do not require ViewRay installation at the ultimate user site, and the distributors may either perform the installation themselves or hire another party to perform the installation. For sales of MRIdian systems for which the Company is not responsible for installation, revenue recognition occurs when the entire system is shipped, which is when the control of the system is transferred to the customer.

Service revenue is derived primarily from maintenance services. The maintenance and support service is a stand-ready obligation which is performed over the term of the arrangement and, as a result, service revenue is recognized ratably over the service period as the customers benefit from the service throughout the service period.

In December 2014, the Company entered into a distribution agreement with Itochu Corporation pursuant to which it appointed Itochu as its exclusive distributor for the promotion, sale and delivery of MRIdian products within Japan. In consideration of the exclusive distribution rights granted, the Company received $4.0 million, which was recorded as deferred revenue. Starting in August 2016, distribution rights revenue is recognized ratably over the remaining term of the distribution agreement of approximately 8.5 years. A time-elapsed method is used to measure progress because the control is transferred evenly over the remaining contractual period.

The timing of revenue recognition, billings and cash collections results in short-term and long-term trade receivables, customer deposits, deferred revenues and deferred cost of revenue on the consolidated balance sheets.

Trade receivables are recorded at the original invoiced amount, net of an estimated allowance for doubtful accounts. Trade credit is generally extended on a short-term basis. The Company occasionally provides for long-term trade credit for its maintenance services so that the period between when the services are rendered to its customers and when the customers pay for that service is within one year. Thus, the Company’s trade receivables do not bear interest or contain a significant financing component. Long-term trade receivables of $0.2 million and $0.4 million were reported within other assets in the consolidated balance sheets at December 31, 2019 and 2018, respectively. These amounts are billed in accordance with the terms of the customer contracts to which they relate and are expected to be collected three to four years from the date of invoice as the underlying maintenance services are rendered. At times, billing occurs subsequent to revenue recognition, resulting in an unbilled receivable which represents a contract asset. This contract asset is recorded as an unbilled receivable and reported as part of accounts receivable on the consolidated balance sheets.

Trade receivables are periodically evaluated for collectability based on past credit history of the respective customers and their current financial condition. Changes in the estimated collectability of trade receivables are included in the results of operations for the period in which the estimate is revised. Trade receivables that are deemed uncollectible are offset against the allowance for doubtful accounts. The Company generally does not require collateral for trade receivables. There were no allowances for doubtful accounts recorded at December 31, 2019 or 2018.

Customer deposits represent payments received in advance of system installation. For domestic and international sales, advance payments received prior to inventory shipments are recorded as customer deposits. Advance payments are subsequently reclassified to deferred revenue upon inventory shipment. All customer deposits, including those that are expected to be a deposit for more than one year, are classified as current liabilities based on consideration of the Company’s normal operating cycle (the time between acquisition of the inventory components and the final cash collection from customers on these inventory components) which is in excess of one year.

Deferred revenue consists of deferred product revenue and deferred service revenue. Deferred product revenue arises from timing differences between the fulfillment of contract obligations and satisfaction of all revenue recognition criteria consistent with the Company’s revenue recognition policy. Deferred service revenue results from the advance billing for services to be delivered over a period of time. Deferred revenues expected to be realized within one year or normal operating cycle are classified as current liabilities.

Deferred cost of revenue consists of cost for inventory items that have been shipped, but revenue recognition has not yet occurred. Deferred cost of revenue is included as part of current assets as the corresponding deferred product revenue is expected to be realized within one year or the Company’s normal operating cycle.

During the years ended December 31, 2019, 2018 and 2017, the Company recognized $10.9 million, $19.9 million and $6.6 million, respectively, of revenues that were included in the deferred revenue balance at the beginning of each reporting period.

The Company records revenue from customers in an amount that reflects the transaction price it expects to be entitled to after transferring control of those goods or services. The Company estimates the transaction price at contract inception, including any variable consideration, and updates the estimate each reporting period for any changes. For the year ended December 31, 2019, the Company recognized $0.9 million in revenue from performance obligations satisfied in a prior period. The cumulative catch-up adjustment resulted from a change in transaction price related to variable consideration that was constrained in prior periods.