Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
OPERATING ACTIVITIES:
Net loss	$ (21,351)	$ (13,844)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,354	1,395
Unrealized translation (gains) losses on obligation related to royalty	(144)	206
Non-cash stock-based compensation	3,182	1,277
Non-cash interest expense	0	(3)
Amortization of discounts on marketable securities	(553)	(78)
Changes in operating assets and liabilities:
Accounts receivable	11,608	623
Inventory	(1,120)	321
Prepaid expenses and other current assets	(947)	(1,312)
Other assets	(833)	255
Accounts payable	(2,610)	1,989
Accrued compensation	1,697	(608)
Accrued expenses and other current liabilities	2,308	1,108
Deferred rent	1,131	621
Deferred revenue	975	1,491
Net cash used in operating activities	(4,303)	(6,559)
INVESTING ACTIVITIES:
Purchase of marketable securities	(45,966)	(19,634)
Maturity of marketable securities	64,000	32,125
Purchase of property and equipment	(2,705)	(4,021)
Net cash provided by investing activities	15,329	8,470
FINANCING ACTIVITIES:
Payments made on royalty obligations	(73)	0
Payments made on capital lease obligations	(21)	(47)
Proceeds from issuance of common stock upon exercise of stock options	538	1,310
Proceeds from issuance of common stock upon the exercise of warrants	0	4
Proceeds from issuances of common stock under employee stock purchase plan	1,933	0
Payment of offering costs related to initial public offering	(89)	0
Net cash provided by financing activities	2,288	1,267
Net effect of foreign exchange rate changes on cash, cash equivalents, and restricted cash	(69)	0
Net increase in cash, cash equivalents and restricted cash	13,245	3,178
Cash, cash equivalents and restricted cash - Beginning of period	140,544	72,596
Cash, cash equivalents and restricted cash - End of period	153,789	75,774
Supplemental Disclosures of Cash Flow Information:
Cash paid for interest	293	30
Cash paid for income taxes	(48)	0
Supplemental Disclosures of Noncash Investing and Financing Activities:
Purchases of property and equipment included in accounts payable and accrued expenses	$ 490	$ 3,351