Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (54,568)	$ (50,378)	$ (29,740)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,445	2,269	1,597
Stock-based compensation	26,241	16,329	9,752
Amortization of debt discount and issuance costs	37	210	260
Accretion of discounts on investments, net of premium amortization	(884)	(907)	(352)
Loss on disposal of assets	0	75	9
Provision for bad debt and contractual allowance	24,647	16,448	9,222
Non-cash interest expense	0	0	1,550
Loss on extinguishment of debt	0	3,029	0
Repayment of interest paid in kind	0	(3,141)	0
Cost of operating lease right-of-use assets	8,953	0	0
Changes in operating assets and liabilities:
Accounts receivable	(28,725)	(21,747)	(12,471)
Inventory	(1,974)	(380)	(293)
Prepaid expenses and other current assets	(696)	(1,568)	(795)
Other assets	(4,732)	269	(467)
Accounts payable	5,604	(192)	634
Accrued liabilities	6,002	10,501	5,757
Deferred rent	0	105	135
Deferred revenue	28	(15)	291
Operating lease liabilities	(5,241)	0	0
Net cash used in operating activities	(21,863)	(29,093)	(14,911)
Cash flows from investing activities
Purchases of property and equipment	(20,457)	(5,180)	(3,562)
Purchases of available-for-sale investments	(165,915)	(93,133)	(129,829)
Sales of available-for-sale investments	1,498	5,962	0
Maturities of available-for-sale investments	95,600	126,493	98,707
Net cash provided by (used in) investing activities	(89,274)	34,142	(34,684)
Cash flows from financing activities
Issuance of common stock in connection with follow-on public offering, net	107,369	0	0
Proceeds from issuance of common stock	9,495	9,319	6,390
Tax withholding upon vesting of restricted stock awards	(5,288)	(3,877)	(46)
Payments of deferred offering costs	0	0	188
Proceeds from long-term debt, net of debt discount	0	35,000	0
Repayments of long-term debt	0	(31,500)	0
Payments of issuance costs for long term debt	0	(121)	0
Premiums paid on extinguishment of debt	0	(2,518)	0
Net cash provided by financing activities	111,576	6,303	6,532
Net increase (decrease) in cash and cash equivalents	439	11,352	(43,063)
Cash and cash equivalents, beginning of year	20,023	8,671	51,734
Cash and cash equivalents, end of  year	20,462	20,023	8,671
Supplemental disclosures of cash flow information
Interest paid	1,644	6,065	1,550
Non-cash investing and financing activities
Property and equipment included in accounts payable and accrued liabilities	293	101	110
Deferred offering costs included in accounts payable and accrued liabilities	77	0	0
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 88,860	$ 0	$ 0