Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 276,323,023		$ 258,829,882
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	74,858,551		68,853,761
Gain on disposal of assets	(163,984)		(10,900)
Loss on disposal of assets	288,323		796,234
Gain on sale of investments	(1,028,505)		(3,170,455)
Loss on sale of investments	113,091		3,512,544
Deferred income taxes	6,855,507		2,204,030
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	13,090,804		14,503,307
Change in operating assets and liabilities:
Accounts receivable, net	(28,914,071)		(33,267,389)
Inventories	(17,346,380)		(4,658,192)
Prepaid expenses and other	14,540,408		21,515,247
Accounts payable	(60,096)		4,647,045
Accrued liabilities, excluding dividends declared and short-term debt	13,999,423		22,661,540
Net cash provided by operating activities	352,556,094		356,416,654
Activity in available-for-sale securities:
Sales proceeds	2,888,493		75,741,184
Maturities and calls	18,100,000		0
Purchases	(18,062,164)		(182,664,625)
Plant and equipment additions	(86,111,836)		(91,497,229)
Proceeds from sale of plant and equipment	192,756		516,667
Decrease (Increase) in other assets	2,432,320		(2,416,610)
Net cash used for investing activities	(80,560,431)		(200,320,613)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of debt	(78,125,000)		(30,625,000)
Issuance of common stock from stock plan transactions	31,896,752		55,449,028
Cash dividends paid	(80,417,057)		(75,217,692)
Repurchases of common stock	(129,827,666)		(122,741,623)
Net cash used for financing activities	(256,472,971)		(173,135,287)
NET INCREASE IN CASH AND CASH EQUIVALENTS	15,522,692		(17,039,246)
CASH AND CASH EQUIVALENTS, beginning of period	546,477,075	[1]	551,557,527
CASH AND CASH EQUIVALENTS, end of period	$ 561,999,767		$ 534,518,281

[1] Note: The condensed consolidated balance sheet at December 31, 2016 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.