Profit Sharing Plan and Retirement Plan	12 Months Ended
	Dec. 31, 2020
Profit Sharing Plan and Retirement Plan [Abstract]
Profit Sharing Plan and Retirement Plan	Profit Sharing Plan and Retirement PlanWe have retirement savings plans (the “Retirement Savings Plans”) for substantially all employees who have completed one year of service and are 19 years of age or older. Employees may make 401(k) contributions subject to Internal Revenue Code limitations. The Retirement Savings Plans provide for a discretionary profit sharing contribution to non-driver employees and a matching contribution of a discretionary percentage to driver employees ("Heartland Plan"). Following the acquisition of Millis Transfer on August 26, 2019 a retirement savings plan ("Millis Transfer Plan") was created. The Millis Transfer Plan has the aforementioned characteristics of the Heartland Plan, but is for Millis Transfer employees. Our contributions to the Retirement Savings Plans totaled approximately $2.3 million, $1.6 million, and $1.0 million, for the years ended December 31, 2020, 2019 and 2018, respectively.