Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 17,115,988	$ 13,869,585
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	202,875	1,984,577
Stock-based compensation expense	520,387	159,883
Deferred tax expense	199,908	128,418
Extinguishment of accrued liabilities	0	(78,138)
Changes in operating assets and liabilities:
Accounts receivable	(1,250,070)	(2,245,522)
Income tax payable / receivable	(949,791)	(774,624)
Prepaid expenses and other current assets	(189,959)	(178,453)
Patent costs	(189,704)	(95,399)
Accounts payable and accrued expenses	(921,360)	(356,548)
Deferred revenue	0	(139,680)
Net cash provided by operating activities	14,538,274	12,274,099
Cash flows from investing activities:
Maturity of marketable investments	76,636,059	58,380,000
Purchases of marketable investments	(93,357,599)	(64,618,676)
Net cash used in investing activities	(16,721,540)	(6,238,676)
Cash flows from financing activities:
Proceeds from stock option exercises	2,133,396	2,570,830
Payments for repurchase of common stock	(357,289)	(2,559,050)
Net cash provided by financing activities	1,776,107	11,780
Increase (decrease) in cash and cash equivalents	(407,159)	6,047,203
Cash and cash equivalents at beginning of year	13,176,452	7,333,810
Cash and cash equivalents at end of period	12,769,293	13,381,013
Cash paid during the period for:
Interest	0	0
Taxes	$ 4,462,362	$ 3,917,572