Commitments and Contingencies (a) Operating Leases We have a ground lease obligation on 2010 East Centennial Circle that expires in 2082. After February 2036, rent for the remaining term of the 2010 East Centennial Circle ground lease will be determined based on a fair market value appraisal of the property and, as result, rent after February 2036 is excluded from the minimum commitment information below. We have ground leases on Paul van Vlissingenstraat 16that expires in 2054, Chemin de l Epinglier 2that expires in 2074, Clonshaugh Industrial Estate I and II that expires in 2981, Manchester Technopark that expires in 2125, 29A International Business Park that expires in 2038, Gyroscoopweg 2E-2F, which has a continuous ground lease and will be adjusted on January 1, 2042, and Naritaweg 52, which has a continuous ground lease. In late 2011, we executed a lease for a new location for our headquarters, which began in May 2012, with a lease term of 12 years with an option to extend the lease for an additional five years. We also have operating leases at 111 8 th Avenue (2 nd and 6 th floors), 8100 Boone Boulevard, 111 8t h Avenue (3 rd and 7 th floors) and 410 Commerce Boulevard, which expire in June 2024, September 2017, February 2022 and December 2026, respectively. The lease at 111 8 th Avenue (2 nd and 6 th floors) has an option to extend the lease until June 2034 and the lease at 111 8t h Avenue (3 rd and 7 th floors) has an option to extend the lease until February 2032. The leases at 8100 Boone Boulevard and 410 Commerce Boulevard have no extension options. We have a fully prepaid ground lease on 2055 E. Technology Circle that expires in 2083. We have a fully prepaid ground lease on Cateringweg 5 that expires in 2059. The ground lease at Naritaweg 52 has been prepaid through December 2036. Rental expense for these leases was approximately $16.2 million , $23.1 million , and $10.2 million for the years ended December 31, 2014 , 2013 and 2012 respectively. In 2013, a non-cash $10.0 million straight-line rent ex