Condensed Consolidated Statements of Cash Flows (USD $)	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 80,805,051	$ 66,519,460
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	21,283,279	19,553,096
(Gain) loss on disposal of assets	539,865	439,689
(Gain) loss on sale of investments	(5,177,464)	(3,463,538)
Impairment loss on available-for-sale securities	0	0
Deferred income taxes	7,328,085	301,435
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	6,419,575	4,870,212
Excess tax benefits from stock-based compensation	(2,599,659)	(497,436)
Change in operating assets and liabilities:
Accounts receivable, net	(16,211,416)	(22,294,349)
Inventories	(18,728,798)	(25,671,717)
Prepaid expenses and other	765,712	2,655,958
Accounts payable	22,987,528	16,806,867
Accrued liabilities, excluding dividends declared	7,203,272	7,886,131
Net cash provided by (used for) operating activities	104,615,030	67,105,808
CASH FLOWS FROM INVESTING ACTIVITIES:
Plant and equipment additions	(48,995,466)	(19,095,284)
Proceeds from sale of plant and equipment	77,509	261,328
(Increase) decrease in investments	53,504,964	(78,992,662)
(Increase) decrease in other assets	2,474,000	(5,483,679)
Net cash provided by (used for) investing activities	7,061,007	(103,310,297)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock from stock plan transactions	14,775,493	25,392,689
Cash dividends paid	(32,781,030)	(30,559,224)
Excess tax benefits from stock-based compensation	2,599,659	497,436
Net cash provided by (used for) financing activities	(15,405,878)	(4,669,099)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	96,270,159	(40,873,588)
CASH AND CASH EQUIVALENTS, beginning of period	348,349,773	336,108,446
CASH AND CASH EQUIVALENTS, end of period	$ 444,619,932	$ 295,234,858