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	$ 74.4	$ 117.0
Reconciliation of net income to net cash provided by operating activities:
Share-based compensation expense	61.5	52.3
Depreciation	5.1	4.2
Amortization of debt discount	7.9	10.0
Amortization of debt issuance costs	0.6	0.7
Change in fair value of equity security investments	(0.7)	5.2
Deferred income taxes	3.3	0.0
Other	5.6	0.7
Change in operating assets and liabilities:
Accounts receivable	(1.4)	(21.8)
Inventories	(0.3)	(4.7)
Accounts payable and accrued liabilities	29.0	(5.1)
Other assets and liabilities, net	5.5	(4.1)
Net cash provided by operating activities	190.5	154.4
Cash Flows from Investing Activities:
Purchases of debt securities available-for-sale	(383.1)	(288.6)
Sales and maturities of debt securities available-for-sale	364.2	421.2
Purchases of property and equipment	(8.8)	(6.0)
Net cash (used in) provided by investing activities	(27.7)	126.6
Cash Flows from Financing Activities:
Issuances of common stock under benefit plans	18.2	21.8
Partial repurchase of convertible senior notes	(0.1)	0.0
Net cash provided by financing activities	18.1	21.8
Change in cash, cash equivalents and restricted cash	180.9	302.8
Cash, cash equivalents and restricted cash at beginning of period	190.3	115.5
Cash, cash equivalents and restricted cash at end of period	371.2	418.3
Supplemental Disclosure:
Non-cash capital expenditures	2.2	0.9
Right-of-use assets acquired through operating leases	21.6	0.0
Cash paid for interest	4.3	5.8
Cash paid for income taxes	$ 1.6	$ 0.0