Condensed Statements of Cash Flows - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating activities
Net loss			$ (9,482,676)	$ (11,657,176)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	$ 422,140	$ 291,421	778,344	587,466
Accretion of discount on NuvoGen obligation			(6,006)	99,377
Provision for excess inventory	12,253	51,599	23,533	244,026
Amortization of Growth Term Loan discount and issuance costs			62,951	231,319
Loss on extinguishment of Growth Term Loan			105,064
Amortization of QNAH Convertible Note issuance costs			6,727
Amortization of MidCap Credit Facility discount and issuance costs			48,092
Stock-based compensation expense			1,385,378	814,583
Employee stock purchase plan expense			28,906	29,223
Accretion of incentive from landlord			(71,000)	(71,000)
Accrued interest on available-for-sale securities investments			(187,946)	5,991
Changes in operating assets and liabilities:
Accounts receivable			2,874,274	(173,427)
Inventory			191,836	(19,673)
Prepaid expenses and other			(402,102)	(35,103)
Deferred offering costs			2,953	49,630
Accounts payable			(656,645)	480,025
Accrued liabilities			(1,319,010)	(456,675)
Contract liabilities			(389,172)	278,310
Net cash used in operating activities			(7,006,499)	(9,593,104)
Investing activities
Purchase of property and equipment			(829,186)	(152,339)
Sales, redemptions and maturities of available-for-sale securities			3,300,000	4,300,000
Purchase of available-for-sale securities			(38,079,329)
Net cash (used in) provided by investing activities			(35,608,515)	4,147,661
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)	(3,126,629)
Payments for extinguishment of Growth Term Loan			(4,276,988)
Proceeds from public offering, net			37,932,290
Public offering costs			(207,974)
Proceeds from ATM Offering, net			556,706	14,705,770
Payments on NuvoGen obligation			(435,093)	(400,000)
Payments on capital leases			(40,017)	(24,796)
Proceeds from exercise of stock options			69,513	109,786
Taxes paid for net share settlement of restricted stock awards			(133,513)
Proceeds from shares purchased under the stock purchase plan			62,862	71,689
Net cash provided by financing activities			38,420,770	11,335,820
Increase (decrease) in cash and cash equivalents			(4,194,244)	5,890,377
Cash and cash equivalents at beginning of period			9,968,600	7,507,659	$ 7,507,659
Cash and cash equivalents at end of period	$ 5,774,356	$ 13,398,036	5,774,356	13,398,036	$ 9,968,600
Noncash investing and financing activities
Fixed asset purchases payable and accrued at period end			2,730	72,224
Deferred offering costs payable and accrued at period end				30,000
Carrying value of demonstration units transferred from property and equipment to inventory			49,245	26,807
Equipment purchased through capital lease			45,896
MidCap Term Loan fees and warrant discount			389,000
Retirement of treasury stock				75,000
Supplemental cash flow information
Cash paid for interest			202,573	417,782
Cash paid for taxes			$ 3,545	$ 280