Our leases expire from 2018 through 2028 and have an average term of 4.8 years, although our typical lease term ranges from three to five years. We believe we will not have any difficulty obtaining renewals of leases as they expire or, alternatively, leasing comparable properties. The aggregate annual rent expense under all leases was approximately $40.8 million in 2017.
The decline in fourth quarter 2017 segment revenues compared to the prior year quarter was primarily due to the divestitures from certain ancillary services lines of business at the end of 2016 and lower revenues generated by the valuation services operations in the current year quarter.
Our most critical accounting estimate is the provision for title loss reserves.
In addition to title policy claims, we incur losses in our direct operations from escrow, closing and disbursement functions. These escrow losses typically relate to errors or other miscalculations of amounts to be paid at closing, including timing or amount of a mortgage payoff, payment of property or other taxes and payment of homeowners’ association fees. Escrow losses also arise in cases of mortgage fraud, and in those cases the title insurer incurs the loss under its obligation to ensure that an unencumbered title is conveyed. Escrow losses are recognized as expense when discovered or when contingencies associated with them (such as litigation) are resolved and are typically paid less than 12 months after the loss is recognized. For the years ended December 31, 2017, 2016 and 2015, we accrued approximately $5.0 million, $8.3 million and $11.5 million, respectively, for policy loss reserves relating to escrow losses arising principally from mortgage fraud.
Internal controls relating to independent agencies include, but are not limited to, periodic audits, site visits and reconciliations of policy inventories and premiums. The audits and site visits cover examination of the escrow account bank reconciliations and an examination of a sample of closed transactions. In some instances, the scope of our review is limited by attorney agencies that cite client confidentiality. Certain states have mandated annual reviews of all agencies by their underwriter. We also determine whether our independent agencies have appropriate internal controls as defined by the American Land Title Association's best practices and us. However, even with adequate internal controls in place, their effectiveness can be circumvented by collusion or improper override of the controls by management at the independent agencies. To aid in the selection of independent agencies to review, we have developed an agency risk model that aggregates data from different areas to identify possible problems. This is not a guarantee that all independent agencies with deficiencies will be identified. In addition, we are typically not the only underwriter for which an independent agency issues policies, and independent agencies may not always provide complete financial records for our review. Due to improved agency internal controls as well as better overall economic conditions, we did not experience any significant agency defalcation losses during the three years ended December 31, 2017.
Our accruals for revenues on unreported policies from agencies were not material to our consolidated assets or stockholders’ equity as of December 31, 2017 and 2016. The differences between the amounts our agencies have subsequently reported to us compared to our estimated accruals are substantially offset by any differences arising from prior years’ accruals and have been immaterial relative to consolidated assets and stockholders’ equity during each of the three prior years. We believe our process provides the most reliable estimate of the unreported revenues on policies and appropriately reflects the trends in agency policy activity.
The year 2017 generated the highest volumes for the real estate market since 2007 as both new and existing home sales volumes improved 8% and 1%, respectively, from 2016. Although total mortgage originations decreased 11% (primarily due to lower refinancing originations) and average mortgage interest rates were higher in 2017 compared to the prior year, purchase originations improved 9% in 2017 versus 2016. For the three years ended December 31, 2017, average monthly mortgage interest rates (30-year, fixed-rate) have fluctuated from a low of 3.44% in July 2016 to a high of 4.20% in March 2017. For the year 2018, Fannie Mae projects the 30-year mortgage rate to average at 4.0%, comparable to 2017, and new and existing home sales volumes to increase by 8% and 2%, respectively, from 2017.