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Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)
 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Cash flows from operating activities:    
Net income $ 2,150,095 $ 2,879,431
Adjustments to reconcile net income to net cash flows from operating activities:    
Depreciation and amortization expense 441,199 527,301
Stock-based compensation - nonemployees 75,444 44,574
Stock-based compensation - employees 315,344 315,513
Excess tax benefit derived from exercise of stock options (854,988) (1,516,569)
Noncash interest expense 12,038 123,654
Net unrealized investment gains (34,604)  
Net changes in assets and liabilities affecting operating activities:    
Accounts receivable 2,091,278 325,760
Inventory (1,541,912) 230,591
Other current assets and other assets (173,889) 704
Accounts payable and other accrued liabilities 1,362,385 2,009,529
Other long-term liabilities (596,911) (5,141)
Net cash provided by operating activities 3,245,479 4,935,347
Cash flows from investing activities:    
Additions to property and equipment (178,886) (105,838)
Purchases of marketable securities (18,356,482)  
Proceeds from marketable securities 145,646  
Additions to patents (519,719) (46,344)
Net cash used in investment activities (18,909,441) (152,182)
Cash flows from financing activities:    
Principal payments on note payable    (1,333,334)
Net borrowings on line of credit (500,000)  
Proceeds from exercise of stock options 545,601 523,507
Excess tax benefit derived from exercise of stock options 854,988 1,516,569
Payments made in connection with repurchase of common shares (3,562,381) (1,551,847)
Net (decrease) increase in cash and cash equivalents (2,661,792) (845,105)
Net increase (decrease) in cash and cash equivalents (18,325,754) 3,938,060
Cash and cash equivalents at beginning of period 70,599,146 65,893,970
Cash and cash equivalents at end of period 52,273,392 69,832,030
Non-cash investing and financing activities:    
Net change in unpaid additions to intangibles, property and equipment $ 73,457 $ 40,070