Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 104.0	$ 58.8
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	44.8	43.0
Amortization of deferred contract costs	31.3	25.1
Depreciation and amortization	17.6	15.7
Amortization of investment premiums (discounts)	(0.6)	(1.1)
Other	4.3	0.3
Changes in operating assets and liabilities:
Accounts receivable—net	69.6	63.6
Inventory	6.7	(2.6)
Prepaid expenses and other current assets	(12.9)	(5.9)
Deferred contract costs	(43.0)	(32.9)
Deferred tax assets	7.1	(8.0)
Other assets	0.9	0.1
Accounts payable	(9.0)	(18.0)
Accrued liabilities	1.8	3.2
Accrued payroll and compensation	1.8	(18.1)
Other liabilities	4.1	(0.9)
Deferred revenue	90.9	79.0
Net cash provided by operating activities	319.4	201.3
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investments	(368.3)	(264.5)
Sales of investments	126.8	8.1
Maturities of investments	277.2	227.6
Purchases of property and equipment	(27.6)	(10.2)
Payments made in connection with business combination, net of cash acquired	(3.1)	0.0
Other	(0.4)	0.0
Net cash provided by (used in) investing activities	4.6	(39.0)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchase and retirement of common stock	(889.9)	(60.4)
Proceeds from issuance of common stock	7.4	34.6
Taxes paid related to net share settlement of equity awards	(37.8)	(32.0)
Other	(0.1)	0.0
Net cash used in financing activities	(920.4)	(57.8)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(596.4)	104.5
CASH AND CASH EQUIVALENTS—Beginning of period	1,222.5	1,112.4
CASH AND CASH EQUIVALENTS—End of period	626.1	1,216.9
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Operating lease liabilities arising from obtaining right-of-use assets	2.4	3.5
Cash paid to settle liability incurred for repurchase of common stock	0.0	4.2
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Transfers of evaluation units from inventory to property and equipment	6.3	4.3
Liability for purchase of property and equipment and asset retirement obligations	25.9	7.6
Liability incurred for repurchase of common stock	$ 10.0	$ 0.0