Share-Based Compensation - Compensation Expense Allocation (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense allocation	$ 3,900,000	$ 3,700,000
Share-based compensation expense paid in cash	0	100,000
Share-based compensation expense capitalized to deferred contract costs	100,000	300,000
Cost of services
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense allocation	1,300,000	1,200,000
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense allocation	2,600,000	2,500,000
Other
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense allocation	$ 0	$ 0