Revenue Recognition All leases on real estate assets held by Columbia Property Trust are classified as operating leases, and the related base rental income is generally recognized on a straight-line basis over the terms of the respective leases. Tenant reimbursements are recognized as revenue in the period that the related operating cost is incurred and are billed to tenants pursuant to the terms of the underlying leases. Rental income and tenant reimbursements collected in advance are recorded as deferred income in the accompanying consolidated balance sheets. Management fees earned by Columbia Property Trust for services provided to certain of its unconsolidated joint ventures are recorded as asset and property management fee income during the period in which such services are provided. Lease termination fees are recorded as other property income and recognized on a straight-line basis from when Columbia Property Trust receives notification of termination through the date the tenant has lost the right to lease the space and Columbia Property Trust has satisfied all obligations under the related lease or lease termination agreement. In conjunction with certain acquisitions, Columbia Property Trust has entered into master lease agreements with various sellers, whereby the sellers are obligated to pay rent pertaining to certain nonrevenue-producing spaces either at the time of, or subsequent to, the property acquisition. These master leases were established at the time of acquisition to mitigate the potential negative effects of lost rental revenues and expense reimbursement income. Columbia Property Trust records payments received under master lease agreements as a reduction of the basis of the underlying property rather than rental income. There were no proceeds received from master leases during 2017 , 2016 , or 2015 . Prior to disposition on January 31, 2017, Columbia Property Trust owned the Key Center Marriott, a full-service hotel, through a taxable REIT subsidiary. Revenues derived from the operations of t