CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net (loss) income	$ (494.6)	$ 244.5
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization	10.3	7.9
Share-based compensation expense (benefit)	29.2	(101.1)
Other	6.7	(0.1)
Changes in operating assets and liabilities:
Accounts receivable	16.0	86.0
Inventories	1.7	6.4
Accounts payable and accrued expenses	(27.7)	22.0
Other assets and liabilities	(169.0)	10.1
Net cash (used in) provided by operating activities	(627.4)	275.7
Cash flows from investing activities:
Purchases of property, plant and equipment	(25.1)	(37.6)
Purchases of held-to-maturity and other investments		(26.9)
Sales/maturities of held-to-maturity investments	37.4	26.8
Purchases of available-for-sale investments	(379.5)	(86.0)
Sales/maturities of available-for-sale investments	313.9	70.0
Purchase of investments in privately-held companies	(7.0)	(5.0)
Net cash used in investing activities	(60.3)	(58.7)
Cash flows from financing activities:
Proceeds from line of credit	800.0
Payments of debt issuance costs		(0.7)
Proceeds from the exercise of stock options	8.8	9.2
Proceeds from the issuance of stock under employee stock purchase plan	2.2	2.1
Restricted stock units withheld for taxes	(1.9)
Net cash provided by financing activities	809.1	10.6
Net increase in cash and cash equivalents	121.4	227.6
Cash and cash equivalents, beginning of period	669.2	705.1
Cash and cash equivalents, end of period	790.6	932.7
Supplemental cash flow information:
Cash paid for interest	9.2	2.3
Cash paid for income taxes	0.9	0.2
Non-cash investing and financing activities:
Non-cash additions to property, plant and equipment	$ 5.8	$ 13.9