Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 4,416,595	$ 3,978,604
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization	153,261	699,703
Stock-based compensation expense	141,788	32,512
Changes in operating assets and liabilities:
Accounts receivable	41,897	(6,955,839)
Income tax payable	1,097,913	1,067,002
Prepaid expenses and other current assets	42,359	42,582
Patent costs	0	(44,598)
Accounts payable and accrued expenses	146,073	308,152
Deferred revenue	0	(4,409)
Net cash provided by (used in) operating activities	6,039,886	(876,291)
Cash flows from investing activities:
Maturity of marketable investments	20,152,229	20,287,000
Purchases of marketable investments	(21,829,557)	(14,318,018)
Net cash (used in) provided by investing activities	(1,677,328)	5,968,982
Cash flows from financing activities:
Proceeds from stock option exercises	58,420	132,400
Net cash provided by financing activities	58,420	132,400
Increase in cash and cash equivalents	4,420,978	5,225,091
Cash and cash equivalents at beginning of year	13,176,452	7,333,810
Cash and cash equivalents at end of period	17,597,430	12,558,901
Cash paid during the period for:
Interest	0	0
Taxes	$ 7,362	$ 0