COMMITMENTS AND CONTINGENCIES Operating Leases Acacia leases certain office space under various operating lease agreements expiring at various dates from 2015 through 2020. Minimum annual rental commitments for operating leases of continuing operations having initial or remaining noncancellable lease terms in excess of one year are as follows (in thousands): Years ending December 31, 2015 $ 1,564 2016 1,595 2017 1,557 2018 1,612 2019 1,669 Thereafter 166 Total minimum lease payments $ 8,163 Rent expense for the years ended December 31, 2014, 2013 and 2012 approximated $1,523,000 , $1,312,000 and $898,000 , respectively. Rental payments are expensed in the statements of operations in the period to which they relate. Scheduled rent increases are amortized on a straight-line basis over the lease term. Inventor Royalties and Contingent Legal Expenses In connection with the investment in certain patents and patent rights, certain of Acacia s operating subsidiaries executed related agreements which grant to the former owners of the respective patents or patent rights, the right to receive inventor royalties based on future net revenues (as defined in the respective agreements) generated as a result of licensing and otherwise enforcing the respective patents or patent portfolios. Acacia s operating subsidiaries may retain the services of law firms that specialize in patent licensing and enforcement and patent law in connection with their licensing and enforcement activities. These law firms may be retained on a contingent fee basis whereby such law firms are paid on a scaled percentage of any negotiated fees, settlements or judgments awarded based on how and when the fees, settlements or judgments are obtained. The economic terms of the inventor agreements, operating agreements and contingent legal fee arrangements associated with the patent portfolios owned or controlled by Acacia s operating subsidiaries, if any, including royalty rates, contingent fee rates and other terms, vary across the patent portfolios owned or