CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash Flows from Operating Activities
Net income	$ 112.9	$ 92.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	43.4	43.0
Stock-based compensation	21.1	16.9
Other	2.8	3.5
Changes in operating assets and liabilities:
Accounts receivable	(36.0)	40.5
Prepaid expenses and income taxes	6.8	13.5
Accounts payable	(5.8)	(0.2)
Accrued payroll and contract professional pay	50.5	(0.1)
Income taxes payable	17.3	16.7
Other	(8.3)	23.8
Net cash provided by operating activities	204.7	250.2
Cash Flows from Investing Activities:
Cash paid for property and equipment	(17.6)	(22.6)
Cash paid for acquisitions, net of cash acquired	(85.8)	(85.5)
Other	0.0	(0.3)
Net cash used in investing activities	(103.4)	(108.4)
Cash Flows from Financing Activities:
Proceeds from long-term debt	0.0	65.5
Principal payments of long-term debt	0.0	(65.5)
Debt issuance and amendment costs	(0.5)	(1.3)
Proceeds from option exercises and employee stock purchase plan	7.7	5.9
Payment of employment taxes related to release of restricted stock awards	(7.1)	(5.9)
Repurchase of common stock	0.0	(27.9)
Net cash provided by (used in) financing activities	0.1	(29.2)
Effect of exchange rate changes on cash and cash equivalents	(0.4)	0.1
Net Increase in Cash and Cash Equivalents	101.0	112.7
Cash and Cash Equivalents at Beginning of Year	274.4	95.2
Cash and Cash Equivalents at End of Period	375.4	207.9
Supplemental Disclosure of Cash Flow Information Cash paid for:
Income Taxes Paid	17.7	5.3
Interest	17.6	19.7
Operating leases	17.2	16.5
Noncash transactions —
Operating lease right of use assets obtained in exchange for operating lease liabilities	$ 1.5	$ 10.4