CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) shares in Millions, $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Cash and cash equivalents	$ 229.7	$ 95.2
Accounts receivable, net	676.5	648.7
Prepaid expenses and income taxes	10.3	29.4
Other current assets	18.2	18.2
Total current assets	934.7	791.5
Property and equipment, net	74.2	73.7
Operating lease right of use assets	93.2	94.6
Identifiable intangible assets, net	496.8	476.5
Goodwill	1,590.9	1,486.9
Other	21.8	18.2
Total assets	3,211.6	2,941.4
Accounts payable	50.1	39.2
Accrued payroll and contract professional pay	236.5	203.2
Operating lease liabilities	31.0	25.8
Other current liabilities	71.8	72.7
Total current liabilities	389.4	340.9
Long-term Debt	1,033.2	1,032.3
Operating Lease, Liability, Noncurrent	70.2	75.7
Deferred income tax liabilities	107.2	98.7
Payroll tax deferral and other	87.4	17.6
Total liabilities	1,687.4	1,565.2
Commitments and Contingencies (Note 6)
Preferred Stock, Value, Issued	0.0	0.0
Common Stock, Value, Issued	0.5	0.5
Paid-in capital	657.7	638.0
Retained earnings	870.9	744.7
Accumulated other comprehensive loss	(4.9)	(7.0)
Total stockholders’ equity	1,524.2	1,376.2
Total liabilities and stockholders’ equity	$ 3,211.6	$ 2,941.4
Common Stock, Shares Outstanding	52.8	52.9
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	75.0	75.0
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized (in shares)	1.0	1.0
Preferred Stock, shares issued (in shares)	0.0	0.0