STATEMENTS OF CASH FLOWS - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Operating activities:      
Net income $ 7,214,545 $ 7,529,920 $ 2,050,366
Adjustments to reconcile net income to net cash provided by operating activities:      
Bad debt expense (benefit) 12,636 3,553 (108,852)
Provision for excess and obsolete inventory 94,186 51,089 62,069
Depreciation and amortization 248,299 223,942 149,056
Excess tax benefit on the exercise of stock options (603,553) (1,728,595) (165,228)
Stock-based compensation 1,841,901 1,220,118 724,063
Impairment of intangible assets   55,433  
Loss (gain) on sale or maturity of investments 83,957 3,575 (7,316)
Changes in operating assets and liabilities:      
Accounts receivable 75,297 (1,906,971) 130,721
Inventory (1,483,361) (308,409) (847,576)
Prepaid expenses and other current assets 4,937 (31,977) (154,912)
Other assets (117,235) (113,959) (15,433)
Deferred income taxes (570,910) (16,116) (167,305)
Accounts payable 1,113 376,293 201,693
Accrued payroll and benefits (252,982) 43,350 589,536
Other accrued taxes 88,407 (35,103) (14,997)
Warranty reserve 6,824 6,156 15,923
Deferred revenue 1,723,918 501,463 186,172
Other current liability 120,634    
Accrued income taxes, net of prepaid income taxes 917,707 1,775,568 (48,188)
Other     5,928
Net cash provided by operating activities 9,406,320 7,649,330 2,585,720
Investing activities:      
Purchases of investments (4,992,626)   (7,951,497)
Proceeds from maturity of investments 4,575,140 253,370 255,109
Purchases of property and equipment (780,809) (298,723) (583,977)
Capitalized intangible assets (743,486) (16,116) (22,311)
Net cash used in investing activities (1,941,781) (61,469) (8,302,676)
Financing activities:      
Proceeds from stock option and warrant exercises 247,133 597,508 105,000
Income tax benefits credited to equity 603,553 1,728,595 165,228
Purchases of treasury stock (9,969,468)    
Repayment of officer note payable     (6,333)
Proceeds from the issuance of common stock pursuant to initial public offering     14,490,000
Payment of initial public offering costs     (2,044,348)
Net cash (used in) provided by financing activities (9,118,782) 2,326,103 12,709,547
Net (decrease) increase in cash and cash equivalents (1,654,243) 9,913,964 6,992,591
Cash and cash equivalents, beginning of year 19,368,114 9,454,150 2,461,559
Cash and cash equivalents, end of year 17,713,871 19,368,114 9,454,150
Supplemental disclosure of cash flow information:      
Cash paid for income taxes $ 3,392,722 $ 2,702,000 $ 1,182,430