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Unaudited Condensed Statements of Cash Flows - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Cash flows from operating activities:    
Net income (loss) $ (1,105,791) $ 385,090
Adjustments to reconcile net income (loss) to net cash used in operating activities:    
Depreciation 121,417 115,447
Amortization 169,346 97,346
Amortization of discounts on investments, net (8,280)  
Stock-based compensation 358,896 73,475
Deferred tax liability 2,592 9,834
Changes in operating assets and liabilities:    
Trade accounts receivable 238,085 (2,357,941)
Inventory 222,869 38,494
Prepaid expenses and other assets (510,637) (75,203)
Accounts payable 246,723 42,917
Accrued bonus (1,505,593) (1,149,076)
Accrued liabilities (40,555) (268,306)
Deferred obligation under operating lease (15,678) (30,739)
Net cash used in operating activities (1,826,606) (3,118,662)
Cash flows from investing activities:    
Purchases of available-for-sale securities (3,724,200)  
Maturities of available-for-sale securities 7,500,000  
Purchases of property and equipment (503,214) (119,312)
Net cash provided by (used in) investing activities 3,272,586 (119,312)
Cash flows from financing activities:    
Repayment of notes payable (333,333) (388,563)
Reversal of costs related to initial public offering   781
Common stock repurchases (779,913)  
Proceeds from exercise of stock options 103,705 323,651
Net cash used in financing activities (1,009,541) (64,131)
Net increase (decrease) in cash and cash equivalents 436,439 (3,302,105)
Cash and cash equivalents, beginning of period 15,026,068 45,161,403
Cash and cash equivalents, end of period 15,462,507 41,859,298
Supplemental disclosure of cash flow information    
Interest paid 15,340 $ 32,508
Taxes paid $ 7,409