19. COMMITMENTS AND CONTINGENCIES Operating Leases   We have entered into operating lease agreements, which expire at various dates through 2022, related to certain machinery and equipment used in our manufacturing process. Rental expense under operating leases amounted to $9.2 million, $7.7 million, and $7.0 million for the years ended December 31, 2012, 2011, and 2010, respectively. The following table, as of December 31, 2012, represents the future minimum rental payments due under non-cancelable operating leases that have initial or remaining lease terms in excess of one year: (Dollars in thousands) 2013 $ 6,649 2014 4,467 2015 2,426 2016 1,068 2017 683 Thereafter 1,056 Total $ 16,349 Purchase obligations   We have entered into unconditional purchase obligations in the ordinary course of business for the purchase of certain raw materials, energy, and services. The following table, as of December 31, 2012, summarizes our unconditional purchase obligations. (Dollars in thousands) 2013 $ 80,535 2014 41,145 2015 44,657 2016 38,672 2017 38,937 Thereafter 177,277 Total $ 421,223 Severance Arrangements   Under our severance policy, and subject to certain terms and conditions, if the employment of a salaried employee or an hourly employee at the Quinnesec mill is terminated under specified circumstances, the employee is eligible to receive a termination allowance based on the employee s applicable service and eligible pay. The termination allowance is equal to two weeks of eligible pay for each full or partial year of applicable service, and in any event is not less than four weeks of eligible pay and not more than 52 weeks of eligible pay. We also may elect to provide the employee with other severance benefits such as prorated and/or reduced incentive awards under our incentive plans and programs, subsidized continuation medical and dental insurance coverage, and outplacement services. Our executive officers are entitled to receive additional severance benefits under their contracts with us in the event of the termi