CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities
Net (loss) income	$ (2,711)	$ 878
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization	1,665	1,009
Loss on disposal of fixed assets	1
Stock-based compensation	5,402	3,202
Unrealized foreign currency gains	(499)	(342)
Amortization of premium on short-term investments	(58)	27
Deferred rent	839	173
Change in operating assets and liabilities:
Accounts receivable, net	(863)	(81)
Inventory	(1,490)	(538)
Prepaid expenses and other current assets	(708)	477
Accounts payable and accrued liabilities	(8,056)	(2,316)
Other assets	(160)	(163)
Net cash (used in) provided by operating activities	(6,638)	2,326
Investing activities
Purchases of short-term investments	(27,919)	(26,599)
Proceeds from sale and maturities of short-term investments	24,097	25,257
Purchases of property and equipment	(1,246)	(760)
Net cash used in investing activities	(5,068)	(2,102)
Financing activities
Proceeds from exercise of stock options	1,452	1,970
Share purchases under Employee Stock Purchase Plan	1,388
Net cash provided by financing activities	2,840	1,970
Effect of exchange rate changes on cash and cash equivalents	(55)	(117)
Net (decrease) increase in cash and cash equivalents and restricted cash	(8,921)	2,077
Cash and cash equivalents and restricted cash at beginning of period	24,508	6,574
Cash and cash equivalents and restricted cash at end of period	15,587	8,651
Supplemental disclosures of cash flow information
Taxes paid	$ 3	1
Supplemental schedule of noncash investing and financing activities
Reduction of liability upon vesting of stock options previously exercised for unvested stock		$ 3