Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2016		Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 258,829,882		$ 230,074,303
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	68,853,761		63,709,095
Gain on disposal of assets	(10,900)		(18,052)
Loss on disposal of assets	796,234		360,659
Gain on sale of investments	(3,170,455)		(8,390,451)
Loss on sale of investments	3,512,544		1,828,617
Deferred income taxes	2,204,030		(10,836,858)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	14,503,307		16,534,607
Excess tax benefits from stock-based compensation	(3,391,853)		(2,411,583)
Change in operating assets and liabilities:
Accounts receivable, net	(33,267,389)		(40,194,912)
Inventories	(4,658,192)		(22,846,177)
Prepaid expenses and other	21,515,247		9,106,066
Accounts payable	4,647,045		12,435,275
Accrued liabilities, excluding dividends declared	22,661,540		33,810,991
Net cash provided by operating activities	353,024,801		283,161,580
Activity in available-for-sale securities:
Sales proceeds	75,741,184		45,787,794
Purchases	(182,664,625)		(34,380,942)
Plant and equipment additions	(91,497,229)		(62,282,827)
Proceeds from sale of plant and equipment	516,667		4
Decrease in other assets	(2,416,610)		(1,931,566)
Net cash used for investing activities	(200,320,613)		(52,807,537)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of long-term debt	(30,625,000)		(30,625,000)
Issuance of common stock from stock plan transactions	55,449,028		20,008,358
Cash dividends paid	(75,217,692)		(72,150,137)
Repurchases of common stock	(122,741,623)		(82,900,454)
Excess tax benefits from stock-based compensation	3,391,853		2,411,583
Net cash used for financing activities	(169,743,434)		(163,255,650)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(17,039,246)		67,098,393
CASH AND CASH EQUIVALENTS, beginning of period	551,557,527	[1]	497,429,804
CASH AND CASH EQUIVALENTS, end of period	$ 534,518,281		$ 564,528,197

[1] Note: The condensed consolidated balance sheet at December 31, 2015 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.