Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 204,224,370	$ 325,136,888
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	78,489,026	79,331,513
(Gain) on disposal of assets	(281,542)	(148,376)
Loss on disposal of assets	146,195	495,697
(Gain) on sale of investments	(1,504,757)	(593,351)
Loss on sale of investments	143,370	0
Change in deferred income taxes	(9,559,993)	2,189,818
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	23,266,906	15,927,434
Change in operating assets and liabilities:
Accounts receivable, net	(32,832,997)	(39,570,916)
Inventories	15,659,539	(13,395,196)
Prepaid expenses and other	8,934,297	(2,729,945)
Accounts payable	(7,389,582)	2,499,481
Accrued liabilities, excluding dividends declared and short-term debt	49,749,418	14,797,251
Net cash provided by operating activities	329,044,250	383,940,298
Activity in available-for-sale securities:
Sales proceeds	15,559,590	57,087,935
Maturities and calls	117,172,368	9,714,000
Purchases	(59,933,780)	(66,360,636)
Plant and equipment additions	(37,048,073)	(58,322,472)
Proceeds from sale of plant and equipment	331,465	1,937,207
Acquisition of businesses, net of cash acquired	(8,043,217)	0
Increase in other assets	(3,326,783)	(3,111,644)
Net cash (used for) investing activities	24,711,570	(59,055,610)
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Proceeds from borrowings on Credit Agreement	75,000,000	0
Repayment of borrowings on Credit Agreement	(50,000,000)	0
Issuance of common stock from stock plan transactions	23,677,181	68,221,875
Cash dividends paid	(87,774,635)	(87,217,383)
Repurchases of common stock	(210,480,446)	(262,763,375)
Net cash (used for) financing activities	(249,577,900)	(281,758,883)
NET INCREASE IN CASH AND CASH EQUIVALENTS	104,177,920	43,125,805
CASH AND CASH EQUIVALENTS, beginning of period	296,321,622	217,025,278
CASH AND CASH EQUIVALENTS, end of period	$ 400,499,542	$ 260,151,083