Our healthcare benefit expense (net of employee contributions) for all plans was approximately $5.3 million and $4.4 million for the three months ended June 30, 2019 and 2018, respectively, and $

10.1

million and $

8.8

million for the six months ended June 30, 2019 and 2018, respectively. An accrual for estimated healthcare claims incurred but not reported (“IBNR”) is included within accrued compensation on the Condensed Consolidated Balance Sheets and was $2.7 million and $2.3 million as of June 30, 2019 and December 31, 2018, respectively.

Workers’ compensation expense totaled $3.6 million and $1.5 million for the three months ended June 30, 2019 and 2018, respectively, and $7.8 million and $5.3 million for the six months ended June 30 2019 and 2018, respectively. Workers’ compensation known claims and IBNR reserves included on the Condensed Consolidated Balance Sheets were as follows (in thousands):

We participate in multiple 401(k) plans, whereby we provide a matching contribution of wages deferred by employees and can also make discretionary contributions to each plan. Certain plans allow for discretionary employer contributions only. These plans cover substantially all our eligible employees. We recognized 401(k) plan expenses of $0.4 million and $0.5 million during the three months ended June 30, 2019 and 2018, respectively, and we recognized $1.0 million and $0.9 million for the six months ended June 30, 2019 and 2018, respectively. These expenses are included in administrative expenses on the accompanying Condensed Consolidated Statements of Operations and Comprehensive Income.

We periodically grant shares of our common stock to our board of directors and our employees. During the three and six months ended June 30, 2019 and 2018, we granted approximately eight thousand and five thousand shares of our common stock, respectively, under our Omnibus Incentive Plan to

non-employee

members of our board of directors. The stock issued will vest over a one year service term. Accordingly, we recorded $0.1 million and $0.2 million of compensation expense during the three and six months ended June 30, 2019 and $

thousand of compensation expense during the three and six months ended June 30, 2018.

In addition, we granted approximately

0.1

million shares of our common stock under our 2014 Omnibus Incentive Plan to employees during the three and six months ended June 30, 2019 and 2018. The shares granted during the three and six months ended June 30, 2019 and 2018 vest in

three

equal installments (rounded to the nearest whole share) annually on April 20 through 2022.

During the six months ended June 30, 2019 and 2018, our employees surrendered approximately

thousand and

thousand shares of our common stock, respectively, to satisfy tax withholding obligations arising in connection with the vesting of common stock awards issued under our 2014 Omnibus Incentive Plan. Share-based compensation expense associated with

non-performance

based awards issued to employees was $1.2 million and $2.3 million for the three and six months ended June 30, 2019, respectively, and $1.0 million and $1.9 million for the three and six months ended June 30, 2018, respectively. We recognized excess tax benefits of $

0.3

million for the three and six months ended June 30, 2019 and $0.4 million and $

0.5

million for the three and six months ended June 30, 2018, respectively, within the income tax provision in the Condensed Consolidated Statements of Operations and Comprehensive Income.

As of June 30, 2019, we had $6.9 million of unrecognized compensation expense related to these nonvested common stock awards issued to the board of directors and our employees. This expense is subject to future adjustments for forfeitures and is expected to be recognized on a straight-line basis over the remaining weighted-average period of 2.1 years. Shares forfeited are returned as treasury shares and available for future issuances. See the table below for changes in shares and related weighted average fair market value per share.

During the six months ended June 30, 2019, we issued under our 2014 Omnibus Incentive Plan approximately

thousand shares of our common stock to certain officers, which vest in

two

equal installments on each of April 20, 2020 and April 20, 2021. In addition, during the three months ended June 30, 2019, we established, and our Board of Directors approved, performance-based targets in connection with common stock awards to be issued to certain officers in 2020 contingent upon achievement of these targets. Share-based compensation expense associated with these performance-based awards and prior performance-based grants was $

0.8

million and $

1.5

million for the three and six months ended June 30, 2019, respectively, and $

0.6

million and $

1.0

million for the three and six months ended June 30, 2018, respectively.

As of June 30, 2019, we had $5.0 million of unrecognized compensation expense related to nonvested performance-based common stock awards. This expense is subject to future adjustments for forfeitures and is expected to be recognized over the remaining weighted-average period of 2.0 years using the graded-vesting method. See the table below for changes in shares and related weighted average fair market value per share.

During 2018, we established, and our board of directors approved, performance-based restricted stock units in connection with common stock awards which were issued to certain employees during the six months ended June 30, 2019 based upon achievement of a performance target. In addition, during the six months ended June 30, 2019, we established, and our board of directors approved, performed-based restricted stock units in connection with common stock awards to be issued to certain employees in 2020 based upon achievement of a performance target. These units will be accounted for as equity-based awards that will be settled with a fixed number of common shares. We recorded $

0.2

million and $

0.3

million in compensation expense associated with these performance-based units during the three and six months ended June 30, 2019, respectively, and $

0.3

million and $

1.2

million for the three and six months ended June 30, 2018, respectively.

As of June 30, 2019, we had $0.5 million of unrecognized compensation expense related to nonvested performance-based common stock units. This expense is subject to future adjustments for forfeitures and is expected to be recognized on a straight-line basis over the remaining weighted-average period of 0.8 years. See the table below for changes in shares and related weighted average fair market value per share.

Administrative stock compensation expense includes all stock compensation earned by our administrative personnel, while cost of sales and selling stock compensation represents all stock compensation earned by our installation and sales employees, respectively.