Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (76,643)	$ (35,363)
Adjustments to reconcile net loss to cash flows from operating activities:
Depreciation and amortization	6,370	2,252
Amortization of investment discount	(3,476)	(1,259)
Non-cash interest expense	5,208	4,940
Loss on disposal of assets	88	10
Stock-based compensation	16,139	10,526
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(1,466)	(10,380)
Net increase in inventory	(15,022)	(15,770)
Net (increase) decrease in other assets	(79,564)	4,672
Net decrease in accounts payable, accrued expenses, deferred revenue and other liabilities	2,133	4,704
Net cash used in operating activities	(146,233)	(35,668)
Cash flows from investing activities:
Purchase of property and equipment	(16,263)	(12,166)
Purchase of intangible assets	(855)	(673)
Purchase of available-for-sale securities	(494,481)	(91,514)
Maturity and sale of available-for-sale securities	646,830	90,093
Net cash provided by (used in) investing activities	135,231	(14,260)
Cash flows from financing activities:
Proceeds from revolving line of credit		96,235
Repayment of revolving line of credit		(100,142)
Repayments on mortgage loans		(1,265)
Proceeds from sale of common stock, net of offering costs	365,264
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	12,299	12,643
Net cash provided by financing activities	377,563	7,471
Increase (decrease) in cash, cash equivalents and restricted cash	366,561	(42,457)
Cash, cash equivalents and restricted cash:
Beginning of period	370,829	599,827
End of period	737,390	557,370
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	732,190	557,234
Restricted cash in other assets	$ 5,200	$ 136
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 737,390	$ 557,370
Supplemental disclosure of cash flow information:
Cash paid during the period for interest		853
Supplemental schedule of non-cash investing activities and financing activities:
Shares withheld for taxes	889
Sale of available-for-sale securities included in investment receivable	42,300
Reclassification of long term investments to short term investments		9,980
Intangible assets included in accrued expenses	230	202
Property and equipment included in accrued expenses	$ 2,878	$ 2,980