Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit PlanWe offer the GP Retirement Savings Plan (the “Plan”) to our employees in the U.S. Eligible employees are automatically enrolled unless they elect to not participate in the Plan, and contributions begin as soon as administratively feasible after enrollment.  The Plan permits pre-tax contributions to the Plan by participants pursuant to Section 401(k) of the Internal Revenue Code (IRC).  We make matching contributions at our discretion. In 2020, 2019 and 2018, we contributed 337,371, 219,427, and 162,572 shares, respectively, of our common stock directly to the Plan which had a value of approximately $3.0 million each year, and is recognized as compensation expense in the consolidated statements of operations for matching contributions to the Plan.We also maintain several defined contribution pension plans for our employees in the U.S., United Kingdom and other countries. We contributed to these plans $2.8 million, $2.7 million and $2.7 million during the years ended December 31, 2020, 2019 and 2018, respectively.