Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 8,683,675	$ 8,455,431
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	1,632,823	1,215,814
Stock-based compensation expense	100,428	100,428
Deferred tax expense	298,121	(2,747,864)
Changes in operating assets and liabilities:
Accounts receivable	(871,093)	(1,298,832)
Income tax receivable	437,781	916,843
Prepaid expenses and other current assets	(48,719)	(170,591)
Patent costs	0	(23,341)
Accounts payable and accrued expenses	46,626	380,858
Income taxes payable	0	279,333
Deferred revenue	(907,776)	7,667,163
Net cash provided by operating activities	9,371,866	14,775,242
Cash flows from investing activities:
Maturity of marketable investments	43,579,082	32,548,040
Purchases of marketable investments	(50,933,705)	(47,568,734)
Net cash used in investing activities	(7,354,623)	(15,020,694)
Cash flows from financing activities:
Proceeds from stock option exercises	258,250	529,300
Payments for repurchase of common stock	(616,499)	(898,025)
Excess tax benefits from share-based payment arrangements	0	224,047
Net cash used in financing activities	(358,249)	(144,678)
Increase (decrease) in cash and cash equivalents	1,658,994	(390,130)
Cash and cash equivalents at beginning of year	4,763,364	5,137,875
Cash and cash equivalents at end of period	6,422,358	4,747,745
Cash paid during the period for:
Interest	0	0
Taxes	$ 4,410,000	$ 5,825,000