Condensed Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 128,988,206	$ 124,202,115
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,620,512	33,310,248
(Gain) loss on disposal of assets	327,382	838,359
(Gain) loss on sale of investments	(7,578,955)	(7,390,376)
Deferred income taxes	2,923,004	3,027,961
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	12,361,993	10,184,719
Excess tax benefits from stock-based compensation	(641,072)	(3,361,960)
Change in operating assets and liabilities:
Accounts receivable, net	(15,882,832)	(34,391,598)
Inventories	11,633,857	(50,402,115)
Prepaid expenses and other	4,403,912	6,319,685
Accounts payable	(13,236,250)	29,862,133
Accrued liabilities, excluding dividends declared	15,529,686	13,232,767
Net cash provided by (used for) operating activities	176,449,443	125,431,938
CASH FLOWS FROM INVESTING ACTIVITIES:
Plant and equipment additions	(97,597,283)	(84,994,919)
Proceeds from sale of plant and equipment	1,012,608	177,132
(Increase) decrease in investments	38,774,729	31,358,531
(Increase) decrease in other assets	(16,036,911)	1,560,369
Net cash provided by (used for) investing activities	(73,846,857)	(51,898,887)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock from stock plan transactions	8,417,982	21,815,871
Cash dividends paid	(54,829,734)	(49,955,251)
Repurchases of common stock	(33,716,725)
Excess tax benefits from stock-based compensation	641,072	3,361,960
Net cash provided by (used for) financing activities	(79,487,405)	(24,777,420)
NET INCREASE IN CASH AND CASH EQUIVALENTS	23,115,181	48,755,631
CASH AND CASH EQUIVALENTS, beginning of period	357,986,774	348,349,773
CASH AND CASH EQUIVALENTS, end of period	$ 381,101,955	$ 397,105,404