Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 20,053,269	$ 11,328,266	$ 11,372,239
Adjustments to reconcile net income to net cash provided in operating activities:
Amortization	2,432,941	2,239,551	1,691,539
Stock-based compensation expense	263,431	127,378	133,904
Deferred tax expense	90,176	1,550,416	(2,667,150)
Extinguishment of accrued liabilities	(78,138)	0	0
Changes in operating assets and liabilities:
Accounts receivable	(4,308,855)	(844,313)	(1,262,872)
Income tax receivable / payable	(763,740)	563,444	422,132
Prepaid expenses and other current assets	(23,246)	842	(240,535)
Patent costs	(121,199)	(204,416)	(23,341)
Accounts payable and accrued expenses	325,577	195,349	127,640
Deferred royalty buy-down	0	(600,000)	(600,000)
Deferred revenue	(139,680)	(1,198,863)	7,398,793
Net cash provided by operating activities from operations	17,730,536	13,157,654	16,352,349
Cash flows from investing activities:
Maturities of marketable securities	75,170,817	54,320,741	43,242,679
Purchases of marketable securities	(86,629,358)	(64,687,200)	(59,935,130)
Net cash used in investing activities from operations	(11,458,541)	(10,366,459)	(16,692,451)
Cash flows from financing activities:
Proceeds from stock option exercises	2,570,830	395,750	711,400
Repurchases of common stock	(3,000,183)	(616,499)	(1,048,592)
Excess tax benefits from share-based payment arrangements	0	0	302,783
Net cash used in financing activities	(429,353)	(220,749)	(34,409)
Increase (decrease) in cash and cash equivalents	5,842,642	2,570,446	(374,511)
Cash and cash equivalents at beginning of year	7,333,810	4,763,364	5,137,875
Cash and cash equivalents at end of year	13,176,452	7,333,810	4,763,364
Cash paid during the period for:
Interest	0	0	0
Taxes	$ 5,417,572	$ 5,400,000	$ 7,945,000