CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities:
Net income	$ 409.9	$ 200.3	$ 174.7
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of discontinued operations	(216.9)	0.0	0.0
Depreciation and amortization	89.6	89.7	91.2
Stock-based compensation	52.7	32.3	39.3
Provision for deferred income taxes	(19.7)	1.3	18.9
Write-off of loan costs	0.0	0.0	18.9
Other	6.3	5.9	16.0
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(111.1)	(12.9)	(24.3)
Prepaid expenses and income taxes	(18.2)	6.5	(20.8)
Accounts payable	(23.6)	0.8	(7.3)
Accrued payroll and contract professional pay	67.4	12.6	5.0
Income taxes payable	1.7	(0.3)	(2.2)
Payroll tax deferral and other	(44.4)	88.6	3.8
Net cash provided by operating activities	193.7	424.8	313.2
Cash Flows from Investing Activities
Cash paid for property and equipment	(34.7)	(32.6)	(32.7)
Cash paid for acquisitions, net of cash acquired	(222.8)	(186.2)	(116.4)
Proceeds from Divestiture of Businesses		0.0	0.0
Other	0.2	(0.2)	0.0
Net cash provided by (used in) investing activities	246.5	(219.0)	(149.1)
Cash Flows from Financing Activities
Proceeds from long-term debt	0.0	65.5	653.0
Principal payments of long-term debt	0.0	(65.5)	(736.2)
Debt issuance or amendment costs	(1.4)	(1.2)	(7.8)
Proceeds from option exercises and employee stock purchase plan	14.3	12.1	12.7
Payment of employment taxes related to release of restricted stock awards	(16.0)	(12.0)	(12.2)
Repurchase of common stock	(181.3)	(27.9)	(20.0)
Net cash used in financing activities	(184.4)	(29.0)	(110.5)
Effect of exchange rate changes on cash and cash equivalents	(0.6)	2.4	(0.2)
Net Increase in Cash and Cash Equivalents	255.2	179.2	53.4
Cash and Cash Equivalents at Beginning of Year	274.4	95.2	41.8
Cash and Cash Equivalents at End of Year	529.6	274.4	95.2
Supplemental Disclosure of Cash Flow Information
Income taxes	170.3	64.2	56.6
Interest	35.2	37.6	44.9
Discontinued Operations | Oxford Business
Cash Flows from Investing Activities
Proceeds from Divestiture of Businesses	$ 503.8	$ 0.0	$ 0.0