Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 230,074,303		$ 217,629,700
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	63,709,095		59,747,630
Gain on disposal of assets	(18,052)		(35,000)
Loss on disposal of assets	360,659		411,129
Gain on sale of investments	(8,390,451)		(14,964,192)
Loss on sale of investments	1,828,617		1,081,164
Deferred income taxes	(10,836,858)		225,911
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	16,534,607		15,569,999
Excess tax benefits from stock-based compensation	(2,411,583)		(2,615,892)
Change in operating assets and liabilities:
Accounts receivable, net	(40,194,912)		(43,365,458)
Inventories	(22,846,177)		(15,523,737)
Prepaid expenses and other	9,106,066		(13,414,445)
Accounts payable	12,435,275		12,103,087
Accrued liabilities, excluding dividends declared	33,810,991		10,603,937
Net cash provided by operating activities	283,161,580		227,453,833
Activity in available-for-sale securities:
Sales proceeds	45,787,794		68,958,662
Purchases	(34,380,942)		(63,310,363)
Plant and equipment additions	(62,282,827)		(49,994,352)
Proceeds from sale of plant and equipment	4		35,005
(Increase) in other assets	(1,931,566)		(1,213,792)
Net cash (used for) investing activities	(52,807,537)		(45,524,840)
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Repayment of long-term debt	(30,625,000)		(5,625,000)
Issuance of common stock from stock plan transactions	20,008,358		19,184,437
Cash dividends paid	(72,150,137)		(64,209,453)
Repurchases of common stock	(82,900,454)		(9,999,957)
Excess tax benefits from stock-based compensation	2,411,583		2,615,892
Net cash (used for) financing activities	(163,255,650)		(58,034,081)
NET INCREASE IN CASH AND CASH EQUIVALENTS	67,098,393		123,894,912
CASH AND CASH EQUIVALENTS, beginning of period	497,429,804	[1]	309,591,724
CASH AND CASH EQUIVALENTS, end of period	$ 564,528,197		$ 433,486,636

[1] Note: The condensed consolidated balance sheet at December 31, 2014 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.