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Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (324,277)	$ (192,649)	$ (176,273)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	3,577	2,901	2,438
Amortization of intangible assets	1,249	0	0
Stock-based compensation expense	26,240	18,073	18,039
Amortization of debt issuance costs	1,350	118	281
Loss on extinguishment of debt	2,209	0	0
Accretion of debt discount	15,889	0
Accretion of back-end fee on debt	50	658	171
Changes in operating assets and liabilities:
Accounts receivable	(5,515)	0	0
Inventory	(7,032)	0	0
Prepaid expenses and other assets	(5,514)	(2,783)	191
Accounts payable	3,870	3,604	2,767
Accrued expenses and other	19,916	5,201	3,043
Accrued compensation	10,011	5,260	2,635
Net cash used in operating activities	(257,977)	(159,617)	(146,708)
Investing activities
Purchase of fixed assets	(13,090)	(3,001)	(4,200)
PARI milestone upon FDA approval	(1,724)	0	0
Net cash used in investing activities	(14,814)	(3,001)	(4,200)
Financing activities
Proceeds from issuance of 1.75% convertible senior notes due 2025	450,000	0	0
Payment on extinguishment of debt	(2,835)	0	0
Payment of debt	(55,000)	0	0
Proceeds from issuance of debt	0	0	30,000
Proceeds from issuance of common stock, net	0	377,656	0
Proceeds from exercise of stock options and ESPP	8,815	3,433	1,084
Payment of debt issuance costs	(14,237)	0	(411)
Net cash provided by financing activities	386,743	381,089	30,673
Effect of exchange rates on cash and cash equivalents	(45)	103	(50)
Net increase (decrease) in cash and cash equivalents	113,907	218,574	(120,285)
Cash and cash equivalents at beginning of period	381,165	162,591	282,876
Cash and cash equivalents at end of period	495,072	381,165	162,591
Supplemental disclosures of cash flow information:
Cash paid for interest	6,289	5,165	3,608
Cash paid for taxes, net	$ 154	$ 166	$ 85
1.75% Convertible Senior Note Due 2025 | Convertible Notes Payable
Supplemental disclosures of cash flow information:
Proceeds from issuance of 1.75% convertible senior notes due 2025	1.75%

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Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

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The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

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The cash outflow to acquire asset without physical form usually arising from contractual or other legal rights, excluding goodwill.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

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The cash inflow from the additional capital contribution to the entity.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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