pre_text: RSU Activity We grant RSUs, which represent the right to receive shares of our common stock. Vesting for RSUs is contingent upon the holders’ continued employment with us and may be subject to other conditions (which may include the satisfaction of a performance measure). Also, certain of our performance-based RSUs include a range of shares that may be released at vesting which are above or below the targeted number of RSUs based on actual performance relative to the grant date performance measure. If the vesting conditions are not met, unvested RSUs will be forfeited. Upon vesting of the RSUs, we may withhold shares otherwise deliverable to satisfy tax withholding requirements. The following table summarizes our RSU activity with performance-based RSUs presented at the maximum potential shares that could be earned and issued at vesting (amounts in thousands except per share amounts): Certain of our performance-based RSUs did not have an accounting grant date as of December 31, 2019, as there is not a mutual understanding between the Company and the employee of the performance terms. Generally, these performance terms relate to operating income performance for future years where the performance goals have not yet been set. As of December 31, 2019, there were 3.2 million performance-based RSUs outstanding for which the accounting grant date has not been set, of which 1.9 million were 2019 grants. Accordingly, no grant date fair value was established and the weighted average grant date fair value calculated above for 2019 grants excludes these RSUs. At December 31, 2019, approximately $96 million of total unrecognized compensation cost was related to RSUs and is expected to be recognized over a weighted-average period of 1.64 years. Of the total unrecognized compensation cost, $50 million was related to performance-based RSUs, which is expected to be recognized over a weighted-average period of 1.63 years. The total grant date fair value of vested RSUs was $147 million, $120 million and $64 million for the years ended December 31, 2019, 2018, and 2017, respectively. The income tax benefit from stock option exercises and RSU vestings was $47 million, $94 million, and $160 million for the years ended December 31, 2019, 2018, and 2017, respectively.
table: Number of shares Weighted-Average Grant Date Fair Value
table: Unvested RSUs at December 31, 2018 10,623 $40.39
table: Granted 4,426 45.55
table: Vested (2,758) 47.86
table: Forfeited (2,963) 54.61
table: Unvested RSUs at December 31, 2019 9,328 $32.60
question: Analyse this data from a financial earnings document. What is the change in the number of unvested RSUs between 2018 and 2019?