Item 2. Properties

We conduct business and maintain offices throughout the world. The facility requirements of our businesses are similar across geographic regions and disciplines. We believe that our facilities are adequate for our current operations and are well maintained. Our principal corporate offices are located at 437 Madison Avenue, New York, New York; 1055 Washington Boulevard, Stamford, Connecticut and 525 Okeechobee Boulevard, West Palm Beach, Florida. We also maintain executive offices in London, England; Shanghai, China and Singapore.

We lease substantially all our office space under operating leases that expire at various dates. Lease obligations of our foreign operations are generally denominated in their local currency. Office base rent expense was $287.8 million, $330.4 million and $334.1 million in 2018, 2017 and 2016, respectively, net of rent received from non-cancelable third-party subleases.

Future minimum office base rent under non-cancelable operating leases, net of rent receivable from existing non-cancelable third-party subleases, is (in millions):

See Note 16 to the consolidated financial statements for a description of our lease commitments, which comprise a significant component of our occupancy and other costs. See Note 22 to the consolidated financial statements for a discussion of the impact of the adoption of FASB Accounting Standards Codification Topic 842, Leases.