Share-Based Compensation Plans - Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 45,062	$ 35,172	$ 36,453
Cost of Services
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	3,300	2,200	4,900
Discontinued Operations
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,000	1,100	700
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	23,461	21,810	24,419
PBRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	18,843	11,399	10,275
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0	0	0
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 2,758	$ 1,963	$ 1,759