10. Segment Information
The Company reports financial performance based on its segments, ACI On Premise and ACI On Demand, and analyzes Segment Adjusted EBITDA as a measure of segment profitability.
The Company’s interim Chief Executive Officer is also the chief operating decision maker ("CODM"). The CODM, together with other senior management personnel, focus their review on consolidated financial information and the allocation of resources based on operating results, including revenues and Segment Adjusted EBITDA, for each segment, separate from Corporate operations.
ACI On Premise serves customers who manage their software on site or through a third-party cloud service provider. These onpremise customers use the Company’s software to develop sophisticated solutions, which are often part of a larger system located and managed at the customer specified site. These customers require a level of control and flexibility that ACI On Premise solutions can offer, and they have the resources and expertise to take a lead role in managing these solutions.
ACI On Demand serves the needs of banks, merchants, and billers who use payments to facilitate their core business. These ondemand solutions are maintained and delivered through the cloud via our global data centers and are available in either a singletenant environment for SaaS offerings, or in a multi-tenant environment for PaaS offerings.
Revenue is attributed to the reportable segments based upon the product sold and mechanism for delivery to the customer. Expenses are attributed to the reportable segments in one of three methods, (1) direct costs of the segment, (2) labor costs that can be attributed based upon time tracking for individual products, or (3) costs that are allocated. Allocated costs are generally marketing and sales related activities as well as information technology and facilities related expense for which multiple segments benefit. The Company also allocates certain depreciation costs to the segments.
Segment Adjusted EBITDA is the measure reported to the CODM for purposes of making decisions on allocating resources and assessing the performance of the Company’s segments and, therefore, Segment Adjusted EBITDA is presented in conformity with ASC 280, Segment Reporting. Segment Adjusted EBITDA is defined as earnings (loss) from operations before interest, income tax expense (benefit), depreciation and amortization (“EBITDA”) adjusted to exclude stock-based compensation, and net other income (expense).
Corporate and unallocated expenses consist of the corporate overhead costs that are not allocated to reportable segments. These overhead costs relate to human resources, finance, legal, accounting, merger and acquisition activity, and other costs that are not considered when management evaluates segment performance. For the year ended December 31, 2017, corporate and unallocated expenses included $46.7 million of general and administrative expense for the legal judgment discussed in Note 15, Commitments and Contingencies.
The following is selected financial data for the Company’s reportable segments for the periods indicated (in thousands):
Assets are not allocated to segments, and the Company’s CODM does not evaluate operating segments using discrete asset information.
Table:
 |  | Years Ended December 31, | 
 | 2019 | 2018 | 2017
Revenues |  |  | 
ACI On Premise | $579,334 | $576,755 | $598,590
ACI On Demand | 678,960 | 433,025 | 425,601
Total revenue | $1,258,294 | $1,009,780 | $1,024,191
Segment Adjusted EBITDA |  |  | 
ACI On Premise | $ 321,305 | $ 323,902 | $ 347,094
ACI On Demand | 66,501 | 12,015 | (1,832 )
Depreciation and amortization | (122,569 ) | (97,350 ) | (102,224 )
Stock-based compensation expense | (36,763 ) | (20,360 ) | (13,683 )
Corporate and unallocated expenses | (104,718 ) | (92,296 ) | (144,715 )
Interest, net | (52,066 ) | (30,388 ) | (38,449 )
Other, net | 520 | (3,724 ) | (2,619 )
Income before income taxes | $ 72,210 | $ 91,799 | $ 43,572
Depreciation and amortization |  |  | 
ACI On Premise | $ 11,992 | $ 11,634 | $ 13,094
ACI On Demand | 34,395 | 31,541 | 34,171
Corporate | 76,182 | 54,175 | 54,959
Total depreciation and amortization | $ 122,569 | $ 97,350 | $ 102,224
Stock-based compensation expense |  |  | 
ACI On Premise | $ 7,651 | $ 4,348 | $ 2,234
ACI On Demand | 7,995 | 4,338 | 2,230
Corporate | 21,117 | 11,674 | 9,219
Total stock-based compensation expense | $36,763 | $20,360 | $13,683


Question: Which group of people does ACI on Premise serve?
Answer: customers who manage their software on site or through a third-party cloud service provider.