Share-based payments	6 Months Ended
	Jun. 30, 2021
Share-based Payment Arrangement [Abstract]
Share-based payments	Share-based payments. As part of its incentive compensation program for executives and senior management employees, the Company provides share-based awards, which include time-based restricted units, performance-based restricted stock units, and stock options. 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 and employee service requirement over a period of approximately three years. The stock options vest on each of the first three anniversaries of the grant date at a rate of 20%, 30% and 50%, chronologically, and expire 10 years after the grant date. Each vested stock option can be exercised to purchase a share of the Company's common stock at the strike price set by the Company at the grant date. The compensation expense associated with the share-based awards is calculated based on the fair value of the related award and recognized over the corresponding vesting period.During the first six months of 2021, the aggregate grant-date fair values of restricted stock unit and stock option awards, respectively, were $8.9 million (166,000 units with an average grant price per unit of $53.71) and $1.3 million (139,000 options with an average grant price per option of $9.24 and exercise strike price of $53.24). During the first six months of 2020, the aggregate grant-date fair values of restricted stock unit and stock option awards, respectively, were $2.4 million (60,000 units with an average grant price per unit of $39.76) and $3.4 million (650,000 options with an average grant price per option of $5.32 and exercise strike price of $39.76).