Employee retirement plan	12 Months Ended
	Dec. 31, 2019
Defined Benefit Plan [Abstract]
Employee retirement plan	Employee retirement planWe have a defined contribution retirement plan pursuant to Section 401(k) of the Internal Revenue Code. Substantially all domestic employees with at least 30 days of continuous service are eligible to participate and may contribute up to 15% of their compensation to such plan. The Board of Directors has elected to make matching contributions equal to 50% of employee contributions, which could be applied to up to 8% of each participant’s compensation during 2019, 2018 and 2017. Employees are eligible for matching contributions after one year of continuous service. Company contributions vest immediately. Our policy prohibits participants from direct investment in shares of our common stock within the plan. Company contributions charged to expense were $9.6 million, $9.4 million and $9.5 million in 2019, 2018, and 2017, respectively.