Revenue Recognition Rents that are fixed and determinable are recognized on a straight-line basis over the minimum terms of the leases. Base rent escalation on leases that are dependent upon increases in the Consumer Price Index (CPI) is recognized when known. In addition, most of the Company's tenants are subject to additional rents if gross revenues of the properties exceed certain thresholds defined in the lease agreements (percentage rents). Percentage rents as well as participating interest for those mortgage agreements that contain similar such clauses are recognized at the time when specific triggering events occur as provided by the lease or mortgage agreements. Rental revenue included percentage rents of $2.2 million and $1.1 million for the nine months ended September 30, 2013 and 2012 , respectively. Mortgage and other financing income included participating interest income of $0.9 million and $0.8 million for the nine months ended September 30, 2013 and 2012, respectively. Lease termination fees are recognized when the related leases are canceled and the Company has no obligation to provide services to such former tenants. Termination fees of $8 thousand and $105 thousand were recognized during the nine months ended September 30, 2013 and 2012 , respectively. Direct financing lease income is recognized on the effective interest method to produce a level yield on funds not yet recovered. Estimated unguaranteed residual values at the date of lease inception represent management's initial estimates of fair value of the leased assets at the expiration of the lease, not to exceed original cost. Significant assumptions used in estimating residual values include estimated net cash flows over the remaining lease term and expected future real estate values. The Company evaluates on an annual basis (or more frequently, if necessary) the collectability of its direct financing lease receivable and unguaranteed residual value to determine whether they are impaired. A direct financing lease receivable is considered