Condensed Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (14,326,084)	$ (17,038,022)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,126,230	893,334
Accretion of discount on NuvoGen obligation	(9,125)	147,753
Provision for excess inventory	63,840	302,085
Amortization of Growth Term Loan discount and issuance costs	62,951	325,517
Loss on extinguishment of Growth Term Loan	105,064
Amortization of QNAH Convertible Note issuance costs	10,090
Amortization of MidCap Credit Facility discount and issuance costs	92,060
Stock-based compensation expense	1,643,353	1,171,988
Employee stock purchase plan expense	43,932	44,170
Accretion of incentive from landlord	(106,500)	(106,500)
Accrued interest on available-for-sale securities investments	(292,308)	5,991
Other operating adjustments		1,307
Changes in operating assets and liabilities:
Accounts receivable	2,994,935	(1,781,782)
Inventory	24,986	13,944
Prepaid expenses and other	(245,488)	(94,295)
Deferred offering costs	2,953	49,630
Accounts payable	(123,266)	1,521,391
Accrued liabilities	(1,216,171)	327,284
Contract liabilities	(449,911)	469,276
Net cash used in operating activities	(10,598,459)	(13,746,929)
Investing activities
Purchase of property and equipment	(857,899)	(525,437)
Sales, redemptions and maturities of available-for-sale securities	15,800,000	4,300,000
Purchase of available-for-sale securities	(43,129,605)
Net cash (used in) provided by investing activities	(28,187,504)	3,774,563
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)	(4,740,774)
Payments for extinguishment of Growth Term Loan	(4,276,988)
Proceeds from public offering, net	37,932,290
Public offering costs	(207,974)	(231,475)
Proceeds from ATM Offering, net	556,706	16,891,193
Payments on NuvoGen obligation	(729,739)	(600,000)
Payments on capital leases	(59,186)	(43,813)
Proceeds from exercise of stock options	204,173	165,261
Taxes paid for net share settlement of restricted stock awards	(133,513)
Proceeds from shares purchased under stock purchase plans	72,862	71,716
Net cash provided by financing activities	38,251,615	11,512,108
(Decrease) increase in cash, cash equivalents and restricted cash	(534,348)	1,539,742
Cash and cash equivalents at beginning of period	9,968,600	7,507,659
Cash, cash equivalents and restricted cash at end of period	9,434,252	9,047,401
Supplemental disclosure of noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	29,615	410,184
Carrying value of demonstration units transferred from property and equipment to inventory	49,245	55,739
Equipment purchased through capital lease	63,809
MidCap Term Loan fees and warrant discount	389,000
Retirement of treasury stock		75,000
Supplemental cash flow information
Cash paid for interest	369,360	575,480
Cash paid for taxes	$ 3,545	$ 1,023