Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (14,908,348)	$ (14,326,084)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	920,863	1,126,230
Accretion of discount on NuvoGen obligation	(10,273)	(9,125)
Provision for excess inventory	126,582	63,840
Amortization of Growth Term Loan discount and issuance costs		62,951
Loss on extinguishment of Growth Term Loan		105,064
Write-off of ATM offering costs	108,883
Amortization of QNAH Convertible Note issuance costs	10,091	10,090
Amortization of MidCap Credit Facility discount and issuance costs	128,476	92,060
Stock-based compensation expense	845,133	1,643,353
Employee stock purchase plan expense	49,914	43,932
Amortization of operating lease right-of-use assets	329,248
Amortization of incentive from landlord		(106,500)
Accrued interest on available-for-sale securities investments	(231,272)	(292,308)
Changes in operating assets and liabilities:
Accounts receivable	1,079,317	2,994,935
Inventory	(11,715)	24,986
Prepaid expenses and other	(383,643)	(245,488)
Deferred offering costs		2,953
Accounts payable	928,454	(123,266)
Accrued liabilities	(1,526,835)	(1,216,171)
Contract liabilities	152,681	(449,911)
Operating lease liabilities	(446,403)
Net cash used in operating activities	(12,838,847)	(10,598,459)
Investing activities
Purchase of property and equipment	(753,430)	(857,899)
Sales, redemptions and maturities of available-for-sale securities	30,800,000	15,800,000
Purchase of available-for-sale securities	(10,922,764)	(43,129,605)
Net cash provided by (used in) investing activities	19,123,806	(28,187,504)
Financing activities
Proceeds from MidCap Credit Facility		7,000,000
MidCap Credit Facility lender fees		(422,390)
Payments on Growth Term Loan		(1,684,626)
Payments for extinguishment of Growth Term Loan		(4,276,988)
Proceeds from 2018 underwritten public offering, net of underwriting discounts, commissions and costs of $2.6 million		37,724,316
Proceeds from 2019 underwritten public and private offerings, net of underwriting discounts, commissions and costs of $1.7 million	21,102,077
Proceeds from ATM Offering, net		556,706
Payments on NuvoGen obligation	(1,003,634)	(729,739)
Payments on financing leases	(34,928)	(59,186)
Proceeds from exercise of stock options	120,954	204,173
Taxes paid for net share settlement of restricted stock awards	(28,067)	(133,513)
Proceeds from shares purchased under stock purchase plans	82,345	72,862
Payment of deferred offering costs	(139,058)
Net cash provided by financing activities	20,099,689	38,251,615
Effect of exchange rates on cash	29,838
Increase (decrease) in cash, cash equivalents and restricted cash	26,414,486	(534,348)
Cash, cash equivalents and restricted cash at beginning of period	11,702,847	9,968,600
Cash, cash equivalents and restricted cash at end of period	38,117,333	9,434,252
Supplemental disclosure of noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	21,381	29,615
Adoption of ASC 842, Leases	694,352
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,005,085
Offering costs payable and accrued at period end	276,694
Equipment purchased through capital leases		63,809
Carrying value of demonstration units transferred from property and equipment to inventory		49,245
MidCap Term Loan fees and warrant discount		389,000
Supplemental cash flow information
Cash paid for interest	521,538	369,360
Cash paid for taxes	$ 3,170	$ 3,545