Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Feb. 16, 2016	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Net services revenue, from related party		$ 136.2	$ 75.4
Accounts receivable, net - related party		30.9		$ 15.4
Accrued service costs, current		27.8		23.7
Customer deposits, current		0.0		0.0
Refund liabilities, current		0.7		0.5
Deferred revenue (contract liabilities), current		3.8		4.0
Current portion of customer liabilities		32.3		28.2
Refund liabilities, non-current		0.0		0.0
Customer deposits, non-current		0.0		0.0
Deferred revenue (contract liabilities), non-current		14.5		11.5
Non-current portion of customer liabilities		14.5		11.5
Total customer liabilities		46.8		39.7
A&R MPSA Services
Related Party Transaction [Line Items]
Accrued compensation and benefits		0.8		0.5
Investor
Related Party Transaction [Line Items]
Accounts receivable, net - related party		30.9		15.4
Accrued service costs, current		27.8		23.7
Customer deposits, current		0.0		0.0
Refund liabilities, current		0.7		0.5
Deferred revenue (contract liabilities), current		2.9		2.9
Current portion of customer liabilities		31.4		27.1
Refund liabilities, non-current		0.0		0.0
Customer deposits, non-current		0.0		0.0
Deferred revenue (contract liabilities), non-current		14.5		11.5
Non-current portion of customer liabilities		14.5		11.5
Total customer liabilities		$ 45.9		$ 38.6
Redeemable Convertible Preferred Stock
Related Party Transaction [Line Items]
Preferred stock, dividend rate, percentage		8.00%		8.00%
TCP-ASC ACHI Series LLLP | Redeemable Convertible Preferred Stock
Related Party Transaction [Line Items]
Preferred stock, dividend rate, percentage	8.00%	8.00%
TCP-ASC ACHI Series LLLP | Redeemable Convertible Preferred Stock | Investor
Related Party Transaction [Line Items]
Preferred stock, dividend rate, percentage	8.00%	8.00%