Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES:
Net loss	$ (67,851,000)	$ (84,263,000)	$ (83,221,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	11,411,000	7,136,000	5,206,000
Amortization of ROU	2,198,000	0	0
Unrealized translation (gains) losses on obligation related to royalty	(147,000)	(357,000)	980,000
Re-valuation of contingent consideration	300,000	0	0
Non-cash stock-based compensation	16,954,000	6,851,000	3,670,000
Non-cash interest expense	0	(13,000)	685,000
Loss on debt extinguishment	0	0	5,075,000
Amortization of premium (discount) on marketable securities	(2,310,000)	(412,000)	359,000
Benefit from income tax differences	(1,597,000)	0	0
Changes in operating assets and liabilities:
Accounts receivable	(7,389,000)	(22,903,000)	(9,292,000)
Inventory	(6,045,000)	(1,849,000)	(4,518,000)
Prepaid expenses and other current assets	(6,185,000)	(3,663,000)	30,000
Other assets	(2,852,000)	(451,000)	(883,000)
Accounts payable	4,341,000	5,046,000	1,250,000
Accrued compensation	5,571,000	8,075,000	2,348,000
Accrued expenses and other current liabilities	9,213,000	286,000	4,657,000
Long-term operating lease liabilities net of ROU	1,039,000	0	0
Deferred rent	0	1,307,000	204,000
Deferred revenue	(3,861,000)	13,025,000	1,215,000
Other liabilities	76,000	0	0
Net cash used in operating activities	(47,134,000)	(72,185,000)	(72,235,000)
INVESTING ACTIVITIES:
Purchase of marketable securities	(614,290,000)	(287,450,000)	(236,835,000)
Maturity of marketable securities	325,333,000	154,625,000	75,402,000
Business acquisition, net of cash acquired	(7,328,000)	0	0
Purchase of property and equipment	(18,717,000)	(20,203,000)	(6,681,000)
Purchase of intangible assets and capitalized license obligations	(2,500,000)	0	0
Payment in connection with a license agreement	(68,000)	0	(2,302,000)
Net cash used in investing activities	(317,570,000)	(153,028,000)	(170,416,000)
FINANCING ACTIVITIES:
Payment related to settlement of debt and buyout of royalty obligations	(311,000)	0	(25,844,000)
Payments made on capital lease obligations	(128,000)	(443,000)	(244,000)
Proceeds from issuance of convertible preferred stock, net of issuance costs	0	0	319,536,000
Proceeds from issuance of common stock under employee stock purchase plan	6,395,000	0	0
Proceeds from issuance of common stock upon exercise of stock options	11,639,000	3,111,000	753,000
Proceeds from issuance of common stock upon the exercise of warrants	0	45,000	12,000
Repurchase of convertible preferred stock	0	0	(5,335,000)
Repurchase of common stock	0	(172,000)	(7,222,000)
Proceeds from public offerings of common stock	350,432,000	254,006,000	0
Payment of offering costs related to public offerings of common stock	(723,000)	(4,386,000)	0
Net proceeds from issuance of equity interests in redeemable noncontrolling interest	0	41,000,000	0
Net cash provided by financing activities	367,304,000	293,161,000	281,656,000
Net effect of foreign exchange rate changes on cash, cash equivalents, and restricted cash	84,000	0	0
Net increase in cash, cash equivalents and restricted cash	2,684,000	67,948,000	39,005,000
Cash, cash equivalents and restricted cash - Beginning of period	140,544,000	72,596,000	33,591,000
Cash, cash equivalents and restricted cash - End of period	143,228,000	140,544,000	72,596,000
Supplemental Disclosures of Cash Flow Information:
Operating lease liabilities arising from obtaining right-of-use assets	16,714,000	0	0
Cash paid for interest	1,181,000	1,251,000	1,339,000
Cash paid for income taxes	298,000	102,000	26,000
Supplemental Disclosures of Noncash Investing and Financing Activities:
Capitalized license fees financed through future royalty payment	0	0	6,302,000
Increase in purchases of property and equipment included in accounts payable and accrued expenses	3,296,000	897,000	591,000
Vesting of common stock exercised early	95,000
Property and equipment acquired under capital leases	0	0	346,000
Conversion of convertible preferred stock to common stock upon initial public offering	0	499,974,000	0
Initial fair value of contingent consideration at acquisition date	1,065,000	0	0
Deferred offering costs included in accounts payable and accrued expenses	0	89,000	0
Convertible Preferred Stock
Supplemental Disclosures of Noncash Investing and Financing Activities:
Issuance of Series D convertible preferred stock in exchange for a technology license agreement	0	0	1,060,000
Common Stock
Supplemental Disclosures of Noncash Investing and Financing Activities:
Vesting of common stock exercised early	$ 95,000	$ 0	$ 103,000