. additionally , the rights to receive a maximum of 2388125 and 2178388 common shares awarded in 2017 and 2016 , under the new performance shares program , are outstanding and contingent upon the company achieving its performance objectives through 2019 and 2018 , respectively . incentive shares plans also include restricted stock awards which involve distribution of common stock to key management employees subject to cliff vesting at the end of service periods ranging from three to ten years