Unaudited Condensed Consolidated Statements of Cash Flows (USD $)	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 145,292,817		$ 97,527,964
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	39,592,545		27,566,632
Gain on disposal of assets	(35,000)		0
Loss on disposal of assets	374,925		2,010,463
Gain on sale of investments	(12,213,259)		(8,567,087)
Loss on sale of investments	647,520		714,756
Deferred income taxes	667,802		(3,024,452)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	10,147,262		8,077,955
Excess tax benefits from stock-based compensation	(1,403,740)		(1,495,850)
Change in operating assets and liabilities:
Accounts receivable, net	(35,234,410)		(10,607,330)
Inventories	(5,137,710)		43,928,296
Prepaid expenses and other	(7,809,607)		329,541
Accounts payable	(689,646)		589,628
Accrued liabilities, excluding dividends declared	7,906,087		15,235,030
Net cash provided by operating activities	142,105,586		172,285,546
Activity in available-for-sale securities:
Sales proceeds	55,370,528		31,899,490
Maturities and calls	0		6,250,000
Purchases	(52,943,104)		(51,633,929)
Plant and equipment additions	(30,248,002)		(24,067,012)
Proceeds from sale of plant and equipment	35,005		15,510
(Increase) decrease in other assets	(683,656)		(531,456)
Net cash used for investing activities	(28,469,229)		(38,067,397)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of long-term debt	(3,750,000)		0
Issuance of common stock from stock plan transactions	11,576,970		16,030,793
Cash dividends paid	(40,808,322)		(38,701,691)
Excess tax benefits from stock-based compensation	1,403,740		1,495,850
Net cash used for financing activities	(31,577,612)		(21,175,048)
NET INCREASE IN CASH AND CASH EQUIVALENTS	82,058,745		113,043,101
CASH AND CASH EQUIVALENTS, beginning of period	309,591,724	[1]	389,678,664
CASH AND CASH EQUIVALENTS, end of period	$ 391,650,469		$ 502,721,765

[1] Note: The condensed consolidated balance sheet at December 31, 2013 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.