Summary of Significant Accounting Policies - Concentration of Business (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant customers
Net revenue	$ 1,184,960	$ 1,170,117	$ 1,100,075	$ 1,122,379	$ 1,133,775	$ 1,158,543	$ 1,154,289	$ 1,119,006	$ 4,577,531	$ 4,565,613	$ 4,957,522
Accounts receivable, net	$ 743,502				$ 680,569				$ 743,502	680,569	657,734
Minimum
Significant customers
Term of contracts with customers									1 year
Term of contract extensions or renewals									1 year
Notice period for termination of contract									30 days
Maximum
Significant customers
Term of contracts with customers									3 years
Term of contract extensions or renewals									2 years
Notice period for termination of contract									180 days
Pennsylvania Counties
Significant customers
Net revenue									$ 583,000	537,800	544,600
CMS
Significant customers
Net revenue									243,700	287,600	442,300
United States federal government
Significant customers
Net revenue									$ 273,000	$ 299,200	$ 308,700