Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 113,450,870	$ 89,505,801
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,599,131	26,295,146
(Gain) on disposal of assets	(2,391)	(151,910)
Loss on disposal of assets	131,490	54,279
(Gain) on sale of investments	(486,433)	(42,461)
Loss on sale of investments	41,681	5,487
Change in deferred income taxes	(1,544,501)	(1,589,855)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	5,894,645	6,356,070
Change in operating assets and liabilities:
Accounts receivable, net	7,253,692	1,832,201
Inventories	(6,768,464)	(2,064,558)
Prepaid expenses and other	768,229	12,779,046
Accounts payable	22,277,513	2,545,274
Accrued liabilities, excluding dividends declared and short-term debt	24,233,539	15,755,950
Net cash provided by operating activities	190,849,001	151,280,470
Activity in available-for-sale securities:
Sales proceeds	15,019,323	3,124,008
Maturities and calls	2,000,000	19,720,000
Purchases	(31,379,609)	(48,606,718)
Plant and equipment additions	(12,599,388)	(15,574,443)
Proceeds from sale of plant and equipment	17,744	165,533
Acquisition of businesses, net of cash acquired	(12,023,440)	0
Increase in other assets	(1,643,884)	(2,544,554)
Net cash (used for) investing activities	(40,609,254)	(43,716,174)
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Proceeds from borrowings on Credit Agreement	0	75,000,000
Issuance of common stock from stock plan transactions	9,265,840	7,355,488
Cash dividends paid	(29,243,108)	(28,896,894)
Repurchases of common stock	(97,692,763)	(178,819,584)
Net cash (used for) financing activities	(117,670,032)	(125,360,990)
NET INCREASE IN CASH AND CASH EQUIVALENTS	32,569,715	(17,796,694)
CASH AND CASH EQUIVALENTS, beginning of period	423,371,036	296,321,622
CASH AND CASH EQUIVALENTS, end of period	$ 455,940,751	$ 278,524,928