Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 199,957,288	$ 87,131,768
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	51,497,665	53,437,698
(Gain) on disposal of assets	(19,891)	(155,229)
Loss on disposal of assets	133,036	88,357
(Gain) on sale of investments	(969,971)	(1,023,683)
Loss on sale of investments	192,346	72,871
Change in deferred income taxes	(3,546,862)	(2,176,462)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	12,622,158	15,960,362
Change in operating assets and liabilities:
Accounts receivable, net	50,784,339	64,981,864
Inventories	(37,608,133)	(10,710,548)
Prepaid expenses and other	(41,394,722)	14,230,026
Accounts payable	16,477,865	(37,452,944)
Accrued liabilities, excluding dividends declared and short-term debt	4,117,051	6,068,104
Net cash provided by operating activities	252,242,169	190,452,184
Activity in available-for-sale securities:
Sales proceeds	34,250,068	5,607,634
Maturities and calls	16,685,000	90,017,368
Purchases	(71,596,074)	(52,650,769)
Plant and equipment additions	(31,352,443)	(28,828,066)
Proceeds from sale of plant and equipment	99,850	200,475
Acquisition of businesses, net of cash acquired	(12,023,440)	(7,031,827)
Increase in other assets	(458,637)	(3,886,518)
Net cash (used for) provided by investing activities	(64,395,676)	3,428,297
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Proceeds from borrowings on Credit Agreement	0	75,000,000
Issuance of common stock from stock plan transactions	13,656,884	15,710,692
Cash dividends paid	(58,227,768)	(58,281,727)
Repurchases of common stock	(213,613,842)	(178,819,584)
Net cash (used for) financing activities	(258,184,726)	(146,390,619)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(70,338,233)	47,489,862
CASH AND CASH EQUIVALENTS, beginning of period	423,371,036	296,321,622
CASH AND CASH EQUIVALENTS, end of period	$ 353,032,803	$ 343,811,484