Condensed Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (17,038,022)	$ (20,366,469)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	893,334	1,086,752
Accretion of discount on NuvoGen obligation	147,753	156,103
Provision for excess inventory	302,085	437,893
Amortization of Growth Term Loan discount and issuance costs	325,517	415,355
Stock-based compensation expense	1,171,988	552,054
Employee stock purchase plan expense	44,170
Accretion of incentive from landlord	(106,500)	(94,667)
Accrued interest on available-for-sale securities investments	5,991	130,576
Other operating adjustments	1,307
Changes in operating assets and liabilities:
Accounts receivable	(1,781,782)	124,385
Inventory	13,944	(104,277)
Prepaid expenses and other	(94,295)	3,911
Deferred offering costs	49,630
Accounts payable	1,521,391	367,529
Accrued liabilities	327,284	(258,073)
Deferred revenue	469,276	236,187
Net cash used in operating activities	(13,746,929)	(17,312,741)
Investing activities
Purchase of property and equipment	(525,437)	(1,859,155)
Sales, redemptions and maturities of available-for-sale securities	4,300,000	23,000,000
Purchase of available-for-sale securities		(3,381,271)
Net cash provided by investing activities	3,774,563	17,759,574
Financing activities
Payment of offering costs	(231,475)
Proceeds from Growth Term Loan		5,000,000
Payments on Growth Term Loan	(4,740,774)	(2,932,482)
Proceeds from ATM offering	16,891,193
Payments on capital leases	(43,813)	(99,863)
Proceeds from exercise of stock options	165,261	10,132
Proceeds from shares purchased under the stock purchase plan	71,716	167,721
Payments on NuvoGen obligation	(600,000)	(362,500)
Net cash provided by financing activities	11,512,108	1,783,008
Increase in cash and cash equivalents	1,539,742	2,229,841
Cash and cash equivalents at beginning of period	7,507,659	3,293,983
Cash and cash equivalents at end of period	9,047,401	5,523,824
Noncash investing and financing activities
Fixed asset purchases payable and accrued at period end	410,184	25,496
Carrying value of demonstration units transferred from property and equipment to inventory	55,739
Stock issued for settlement of accrued bonus		(364,910)
Purchase of property and equipment under capital lease		226,835
Incentive from landlord		710,000
Retirement of treasury stock	75,000
Supplemental cash flow information
Cash paid for interest	$ 575,480	$ 850,713