2019
2018
2017
Nonvested stock units
$5,458
$5,737
$5,873
Stock options
936
1,790
1,826
Performance share awards
1,417
1,236
2,580
Nonvested restricted stock awards
—
33
88
Non-management directors’ deferred compensation
263
350
270
Total share-based compensation expense
$8,074
$9,146
$10,637
13 .
share-based employee compensation .
stock incentive plans — we offer share-based compensation plans to attract retain and motivate key officers employees and non-employee directors to work toward the financial success of the company .
our stock incentive plans are administered by the compensation committee of the board of directors and have been approved by the stockholders of the company .
the terms and conditions of our share-based awards are determined by the compensation committee for each award date and may include provisions for the exercise price expirations vesting restriction on sales and forfeitures as applicable .
we issue new shares to satisfy stock issuances under our stock incentive plans .
our amended and restated 2004 stock incentive plan authorizes the issuance of up to11600000 common shares in connection with the granting of stock options stock appreciation rights restricted stock purchase rights restricted stock bonuses restricted stock units or performance units to key employees directors and other designated employees .
there were 1677983 shares of common stock available for future issuance under this plan as of september 29 2019 .
we also maintain a deferred compensation plan for non-management directors under which those who are eligible to receive fees or retainers may choose to defer receipt of their compensation .
the deferred amounts are converted to stock equivalents .
the plan requires settlement in shares of our common stock based on the number of stock equivalents and dividend equivalents at the time of a participant ’ s separation from the board of directors .
this plan provides for the issuance of up to 350000 shares of common stock in connection with the crediting of stock equivalents .
there were143122 shares of common stock available for future issuance under this plan as of september 29 2019 .
compensation expense — the components of share-based compensation expense included within “ selling general and administrative expenses ” in our consolidated statement of earnings in each fiscal year are as follows -in thousands : .
nonvested restricted stock units — nonvested restricted stock units - “ rsus ” are generally issued to executives non-management directors and certain other members of management and employees .
prior to fiscal 2011 rsus were granted to certain executive and senior vice presidents pursuant to our share ownership guidelines .
these awards vest upon retirement or termination based on years of service .
there were 60272 of such rsus outstanding as of september 29 2019 .

Question: Which groups of people are generally issued with Nonvested restricted stock units ("RSUs")?

Question: As of September 2019, what is the number of outstanding RSUs?

Question: Under the Amended and Restated 2004 Stock Incentive Plan, how many shares of common stock were available for future issuance as of September 29, 2019?

Question: What is the average stock options from 2017-2019?

Question: What is the difference in the total share-based compensation expense between 2018 and 2019?

Question: In 2019, what is the percentage constitution of nonvested stock units among the total share-based compensation expense?