Share-based payments	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Share-based payments	Share-based payments. Beginning in 2018, the Company grants time-based and performance-based restricted stock units to executives and senior management employees. Each restricted stock unit represents a contractual right to receive a share of the Company's common stock. The time-based units vest on each of the first three anniversaries of the grant date, while the performance-based units vest upon achievement of certain financial objectives over a period of approximately three years. Awards are made pursuant to the Company’s employee incentive compensation plans and the compensation expense associated with the awards is recognized over the corresponding vesting period. The aggregate grant-date fair values of restricted stock unit awards during the first nine months of 2019 and 2018 were $5.0 million (119,000 units with an average grant price per unit of $42.05) and $4.8 million (111,000 units with an average grant price per unit of $43.39), respectively.