At December 31, 2020, the Company’s authorized capital stock consisted of 300,000,000 shares of $0.01 par value common stock and 15,000,000 shares of $0.01 par value preferred stock.

The changes in common shares outstanding during the three years ended December 31, 2018, December 31, 2019, and December 31, 2020 were as follows:

Common Shares Outstanding at December 31, 2017	96,380,102
Issuance of restricted shares	589,736
Treasury stock purchases	(3,785,658	)
Issuance of shares to directors	13,249
Exercise of stock options	425,505
Common Shares Outstanding at December 31, 2018	93,622,934
Issuance of restricted stock and restricted stock units	564,729
Treasury stock purchases	(15,679	)
Vesting of restricted stock and restricted stock units	74,292
Exercise of stock options	215,300
Common Shares Outstanding at December 31, 2019	94,461,576
Issuance of stock as part of debt refinancing	15,942,551
Issuance of shares to directors	81,843
Treasury stock purchases	(21,685	)
Vesting of restricted stock and restricted stock units	203,328
Exercise of stock options	114,000
Common Shares Outstanding at December 31, 2020	110,781,613

During the year ended December 31, 2020, the Company purchased 21,685 treasury shares for $96 from its employees to cover federal and state and other tax withholdings associated with the vesting of restricted stock and restricted stock units. During the year ended December 31, 2019, the Company purchased 15,679 treasury shares for $156 from its employees to cover federal and state and other tax withholdings associated with the vesting of restricted stock and restricted stock units. Additionally, during the year ended December 31, 2018, the Company acquired 3,785,658 treasury shares for $40,197. The shares are included in “common stock held in treasury” in the Company’s consolidated balance sheet.