Share-based payments

3 Months Ended

Mar. 31, 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 the first quarters 2018 and 2017 were $3.9 million (90,000 shares with an average grant price per share of $43.33) and $3.0 million (69,000 shares with an average grant price per share of $43.87), 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.