STOCK-BASED COMPENSATION

Total stock-based compensation cost charged to selling, general and administrative expenses for the three months ended March 31, 2019 and March 31, 2018 was $5.8 million and $3.1 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation was $1.1 million and $0.9 million for the three months ended March 31, 2019 and March 31, 2018, respectively.

Restricted Stock Awards

The following information relates to restricted stock awards that have been granted to employees and directors under the Company's equity incentive plan adopted in 2010 (the "2010 Plan"). The restricted stock awards are not transferable until vested and the restrictions generally lapse upon the achievement of continued employment over a three-to-five-year period or service as a director until the following annual meeting of shareholders. The fair value of each restricted stock grant is based on the closing price of the Company's common stock on the date of grant and is amortized to expense over its vesting period.

The following table summarizes information about restricted stock awards for the three months ended March 31, 2019:



Restricted Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2019	657,240		$	54.65
Granted	42,300		61.18
Vested	(61,391	)	52.83
Forfeited	(21,870	)	54.39
Balance at March 31, 2019	616,279		54.51

As of March 31, 2019, there was $23.1 million of total unrecognized compensation cost arising from restricted stock awards under the Company's 2010 Plan. This cost is expected to be recognized over a weighted average period of 2.6 years. The total fair value of restricted stock vested during the three months ended March 31, 2019 and March 31, 2018 was $3.2 million and $1.3 million, respectively.

Performance Stock Awards

The following information relates to performance stock awards that have been granted to employees under the Company's 2010 Plan. Performance stock awards are subject to performance criteria established by the compensation committee of the Company's board of directors prior to or at the date of grant. The vesting of the performance stock awards is based on achieving such targets typically based on revenue, Adjusted EBITDA margin, Adjusted Free Cash Flow and Total Recordable Incident Rate. In addition, performance stock awards include continued service conditions. The fair value of each performance stock award is based on the closing price of the Company's common stock on the date of grant and is amortized to expense over the service period if achievement of performance measures is considered probable.

The following table summarizes information about performance stock awards for the three months ended March 31, 2019:



Performance Stock	Number of Shares		Weighted Average Grant-Date Fair Value
Balance at January 1, 2019	213,490		$	55.71
Granted	—		—
Vested	(51,996	)	55.77
Forfeited	(14,120	)	55.69
Balance at March 31, 2019	147,374		55.69

As of March 31, 2019, there was $4.6 million of total unrecognized compensation cost arising from unvested performance stock awards deemed probable of vesting under the Company's 2010 Plan. The total fair value of performance awards vested during the three months ended March 31, 2019 and March 31, 2018 was $2.9 million and $0.5 million, respectively.

Common Stock Repurchases

The Company's board of directors has authorized the repurchase of up to $600 million of the Company's common stock. During the three months ended March 31, 2019 and March 31, 2018, the Company repurchased and retired a total of approximately 0.1 million and 0.3 million shares, respectively, of the Company's common stock for total costs of approximately $6.3 million and $14.3 million, respectively. Through March 31, 2019, the Company has repurchased and retired a total of approximately 5.7 million shares of its common stock for approximately $300.3 million under this program. As of March 31, 2019, an additional $299.7 million remained available for repurchase of shares under this program.