Share-based payments

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-based payments

Share-based payments. Prior to 2018, the Company granted executives and senior management shares of restricted common stock, consisting of time-based shares, which vest on each of the first three anniversaries of the grant date, and performance-based shares, which vest upon achievement of certain financial objectives over the period of three years. Starting on January 1, 2018, the Company began granting time-based and performance-based restricted stock units, which have vesting conditions generally similar to those restricted common stock shares awarded previously. Each restricted stock unit represents a contractual right to receive a share of the Company's common stock.

The aggregate grant-date fair values of these awards during 2018 and 2017 were $4.8 million (110,600 shares with an average grant price per share of $43.39) and $5.1 million (120,000 shares with an average grant price per share of $42.55), respectively. Awards were made pursuant to the Company’s employee incentive compensation plans and the compensation expense associated with restricted stock awards is recognized over the corresponding vesting period. Additionally, during the second quarters 2018 and 2017, the Company granted its board of directors, as a component of annual director retainer compensation, 14,300 and 13,000 shares, respectively, of common stock, which vested immediately. The aggregate fair values of these director awards at the grant dates in 2018 and 2017 were both $0.6 million.