We participate in multiple healthcare plans, the largest of which is partially self-funded with an insurance company paying benefits in excess of stop loss limits per individual/family. Our healthcare benefit expense (net of employee contributions) was approximately $5.5 million and $5.6 million for the three months ended September 30, 2020 and 2019, respectively, and $18.2 million and $15.7 million for the nine months ended September 30, 2020 and 2019, respectively, for all plans. An accrual for estimated healthcare claims incurred but not reported (“IBNR”) is included within accrued compensation on the Condensed Consolidated Balance Sheets and was $3.2 million and $2.6 million as of September 30, 2020 and December 31, 2019, respectively.

Workers’ compensation expense totaled $4.1 million and $4.0 million for the three months ended September 30, 2020 and 2019, respectively, and $11.4 million and $11.8 million for the nine months ended September 30, 2020 and 2019, respectively. Workers’ compensation known claims and IBNR reserves included on the Condensed Consolidated Balance Sheets were as follows (in thousands):

We also had an insurance receivable for claims that exceeded the stop loss limit for fully insured policies included on the Condensed Consolidated Balance Sheets. This receivable offsets an equal liability included within the reserve amounts noted above and was 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 September 30, 2020 and 2019, respectively, and $1.6 million and $1.5 million during the nine months ended September 30, 2020 and 2019, 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

non-employee

members of our board of directors and our employees. During the nine months ended September 30, 2020 and 2019, we granted approximately six thousand and eight thousand shares of our common stock, respectively, under our 2014 Omnibus Incentive Plan to

non-employee

members of our board of directors. Substantially all of the stock will vest over a one year service period. Accordingly, we recorded $0.1 million and $0.2 million in compensation expense during the three and nine months ended September 30, 2020, respectively and $0.1 million and $0.3 million for the three and nine months ended September

0, 2019, respectively.

In addition, we granted approximately 0.2 million and 0.1 million shares of our common stock to employees during the nine months ended September 30, 2020 and 2019, respectively. We recorded $1.0 million and $3.0 million of compensation expense associated with

non-performance-based

awards issued to employees during the three and nine months ended September 30, 2020, respectively, and $1.0 million and $3.3 million for the three and nine months ended September

0, 2019, respectively.

During the nine months ended September 30, 2020 and 2019, our employees surrendered approximately 25 thousand and 45 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. We recognized a tax shortfall of $0.3 million for the nine months ended September 30, 2020 and we recognized windfall tax benefits of $0.3 million for the nine months ended September 30, 2019 within the income tax provision in the Condensed Consolidated Statements of Operations and Comprehensive Income.

As of September 30, 2020, we had $7.1 million of unrecognized compensation expense related to these nonvested common stock awards issued to

non-employee

members of our 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 2.0 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 grant date fair value per share.

During the nine months ended September 30, 2020, we issued under our 2014 Omnibus Incentive Plan approximately 0.1 million shares of our common stock to certain officers, which vest in two equal installments on each of April 20, 2021 and April 20, 2022. In addition, during the nine months ended September 30, 2020, we established, and our Board of Directors approved, performance-based targets in connection with common stock awards to be issued to certain officers in 2021 contingent upon achievement of these targets. Share-based compensation expense associated with these performance-based awards and prior performance-based grants was $0.9 million and $2.8 million for the three and nine months ended September 30, 2020, respectively, and $0.8 million and $2.3 million for the three and nine months ended September

0, 2019, respectively.

As of September 30, 2020, 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 1.8 years using the graded-vesting method. See the table below for changes in shares and related weighted average grant date fair value per share.

In addition, there are long-term performance-based restricted stock awards to be issued to certain employees annually through 2022 contingent upon achievement of certain performance targets. These awards are accounted for as liability-based awards since they represent a predominantly-fixed monetary amount that will be settled with a variable number of common shares and as such are included in other long-term liabilities on the Consolidated Balance Sheets. During the three and nine months ended September 30, 2020, we recorded $0.5 million and $1.2 million in compensation expense, respectively, associated with these performance-based awards, and we recorded $0.1 million in compensation expense during the nine months ended September 30, 2019.

During 2019, 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 in 2020 based upon achievement of a performance target. In addition, during the nine months ended September 30, 2020, we established, and our board of directors approved, performance-based restricted stock units in connection with common stock awards to be issued to certain employees in 2021 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 $0.1 million and $0.4 million in compensation expense associated with these performance-based units during the three and nine months ended September 30, 2020, respectively, and $0.2 million and $0.5 million for the three and nine months ended September

0, 2019, respectively.

As of September 30, 2020, we had $0.3 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 0.5 years. See the table below for changes in shares and related weighted average grant date fair 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. The difference between the sum of the expenses described above and the amount in the table is comprised of expenses related to immaterial nonrecurring awards.