the grant date fair value of options is estimated using the black-scholes option-pricing model . the weighted-average assumptions used in valuations for 2017 , 2016 and 2015 are , respectively : risk-free interest rate , based on u.s . treasury yields , 1.7 percent , 1.9 percent and 1.9 percent ; dividend yield , 3.6 percent , 3.8 percent and 3.1 percent ; and expected volatility , based on historical volatility , 24 percent , 27 percent and 28 percent . the expected life of each option awarded is seven years based on historical experience and expected future exercise patterns . perfo rmance shares , restricted stock and restricted stock units the company 2019s incentive shares plans include performance shares awards which distribute the value of common stock to key management employees subject to certain operating performance conditions and other restrictions . the form of distribution is primarily shares of common stock , with a portion in cash . compensation expense for performance shares is recognized over the service period based on the number of shares ultimately expected to be earned . performance shares awards are accounted for as liabilities in accordance with asc 718 , compensation 2013 stock compensation , with compensation expense adjusted at the end of each reporting period to reflect the change in fair value of the awards . as of september 30 , 2016 , 4944575 performance shares awarded primarily in 2013 were outstanding , contingent on the company achieving its performance objectives through 2016 and the provision of additional service by employees . the objectives for these shares were met at the 86 percent level at the end of 2016 , or 4252335 shares . of these , 2549083 shares were distributed in early 2017 as follows : 1393715 issued as shares , 944002 withheld for income taxes , and the value of 211366 paid in cash . an additional 1691986 shares were distributed at the end of 2017 to employees who provided one additional year of service as follows : 1070264 issued as shares , 616734 withheld for income taxes , and the value of 4988 paid in cash . there were 11266 shares canceled and not distributed . 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 . the fair value of restricted stock awards is determined based on the average of the high and low market prices of the company 2019s common stock on the date of grant , with compensation expense recognized ratably over the applicable service period . in 2017 , 130641 shares of restricted stock vested as a result of participants fulfilling the applicable service requirements . consequently , 84398 shares were issued while 46243 shares were withheld for income taxes in accordance with minimum withholding requirements . as of september 30 , 2017 , there were 1194500 shares of unvested restricted stock outstanding . the total fair value of shares vested under incentive shares plans was $ 245 , $ 11 and $ 9 , respectively , in 2017 , 2016 and 2015 , of which $ 101 , $ 4 and $ 5 was paid in cash , primarily for tax withholding . as of september 30 , 2017 , 12.9 million shares remained available for award under incentive shares plans . changes in shares outstanding but not yet earned under incentive shares plans during the year ended september 30 , 2017 follow ( shares in thousands ) : average grant date shares fair value per share .
at the pace of 2017 how many years of issuance remain for the restricted stock plan for non-management directors?
total compensation expense for stock options and incentive shares was $ 115 , $ 159 and $ 30 for 2017 , 2016 and 2015 , respectively , of which $ 5 , $ 14 and $ 6 was included in discontinued operations . the decrease in expense for 2017 reflects the impact of changes in the stock price . the increase in expense for 2016 reflects an increasing stock price in the current year compared with a decreasing price in 2015 , and overlap of awards . income tax benefits recognized in the income statement for these compensation arrangements during 2017 , 2016 and 2015 were $ 33 , $ 45 and $ 2 , respectively . as of september 30 , 2017 , total unrecognized compensation expense related to unvested shares awarded under these plans was $ 149 , which is expected to be recognized over a weighted-average period of 1.5 years . in addition to the employee stock option and incentive shares plans , in 2017 the company awarded 17984 shares of restricted stock and 2248 restricted stock units under the restricted stock plan for non-management directors . as of september 30 , 2017 , 174335 shares were available for issuance under this plan. .