Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Cash Flows [Abstract]
Net loss	$ (9,065)	$ (8,250)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,551	621
Stock-based compensation	305	4,856
Amortization of debt discount and issuance costs	4	26
Accretion of discounts on investments, net of premium amortization	(171)	(227)
Provision for doubtful accounts and contractual allowances	9,184	5,411
Amortization of operating lease right-of-use assets	1,495	1,183
Changes in operating assets and liabilities:
Accounts receivable	(9,989)	(12,392)
Inventory	(191)	(442)
Prepaid expenses and other current assets	114	(29)
Other assets	(2,002)	(365)
Accounts payable	(2,835)	(333)
Accrued liabilities	(9,467)	(6,061)
Deferred revenue	(136)	39
Operating lease liabilities	(1,163)	(1,200)
Net cash used in operating activities	(22,366)	(17,163)
Cash flows from investing activities
Purchases of property and equipment	(3,405)	(1,705)
Purchases of available-for-sale investments	(8,009)	(9,616)
Sales of available-for-sale investments	14,525	0
Maturities of available-for-sale investments	56,800	37,700
Net cash provided by investing activities	59,911	26,379
Cash flows from financing activities
Proceeds from issuance of common stock	2,969	2,120
Tax withholding upon vesting of restricted stock awards	(4,462)	(3,258)
Net cash used in financing activities	(1,493)	(1,138)
Net increase in cash and cash equivalents	36,052	8,078
Cash and cash equivalents beginning of period	20,462	20,023
Cash and cash equivalents end of period	56,514	28,101
Supplemental disclosures of cash flow information
Interest paid	394	411
Non-cash investing and financing activities
Property and equipment costs included in accounts payable and accrued liabilities	136	38
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 621	$ 0