Summary of Significant Accounting Policies - Customers Exceeding Ten Percent of Segment Revenues (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
Revenues	$ 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
Healthcare
Significant customers
Revenues									1,959,869	2,082,088	2,110,756
Healthcare | Customer A
Significant customers
Revenues									344,988	324,321	308,649
Healthcare | Customer B
Significant customers
Revenues									198,199	199,036	169,508
Pharmacy Management
Significant customers
Revenues									2,638,301	2,502,268	2,865,844
Pharmacy Management | Customer C
Significant customers
Revenues									$ 358,236	$ 335,682	$ 344,479