Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
OPERATING ACTIVITIES:
Net loss	$ (81,568)	$ (32,651)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,109	5,011
Amortization of right-of-use assets	3,386	1,633
Charge of in-process research and development costs with no alternative future use	8,500	0
Unrealized translation gains (loss) on obligation related to royalty	0	(51)
Re-valuation of contingent consideration	(190)	0
Non-cash stock-based compensation	32,153	6,398
Amortization of premium (discount) on marketable securities	1,065	(1,276)
Benefit from income tax differences	0	(1,235)
Others	(19)	0
Changes in operating assets and liabilities, net of effect of acquisition:
Accounts receivable, net	6,894	234
Inventory	(5,173)	(5,040)
Prepaid expenses and other current assets	438	1,122
Other assets	(242)	(1,129)
Accounts payable	(2,476)	3,412
Accrued compensation	(31)	701
Accrued expenses and other liabilities	(1,820)	2,939
Operating lease liabilities	(3,881)	1,435
Deferred revenue	(792)	358
Net cash used in operating activities	(36,647)	(18,139)
INVESTING ACTIVITIES:
Purchases of marketable securities	(465,302)	(418,841)
Maturity of marketable securities	197,548	129,160
Business acquisition, net of cash acquired	0	(9,765)
Purchases of property and equipment	(19,105)	(5,752)
Purchase of intangible assets	(17,886)	0
Net cash used in investing activities	(304,745)	(305,198)
FINANCING ACTIVITIES:
Payments made on royalty obligations	0	(151)
Payments made on capital lease obligations	(79)	(62)
Proceeds from issuance of common stock upon exercise of stock options	3,548	5,530
Proceeds from issuances of common stock under employee stock purchase plan	3,956	1,933
Proceeds from public offering, net of underwriting discounts and commissions	355,730	350,432
Payment of offering costs related to public offering	(369)	(326)
Net cash provided by financing activities	362,786	357,356
Net effect of foreign exchange rate changes on cash and cash equivalents	49	90
Net increase in cash and cash equivalents	21,443	34,109
Cash and cash equivalents—Beginning of period	143,228	140,544
Cash and cash equivalents—End of period	164,671	174,653
Supplemental Disclosures of Cash Flow Information:
Operating lease liabilities arising from obtaining right-of-use assets	11,373	1,565
Supplemental Disclosures of Noncash Investing and Financing Activities:
Purchases of property and equipment included in accounts payable and accrued expenses	5,396	3,874
Follow-on public offering issuance costs included in accounts payable and accrued expenses	761	486
Initial fair value of contingent consideration at acquisition date	$ 0	$ 1,135