Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 164,668,228	$ 137,733,969	$ 64,637,085
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42,634,684	38,620,674	38,364,492
Loss on disposal of assets	992,876	1,070,484	659,740
Gain on sale of investments	(15,787,691)	(9,767,008)	(5,363,090)
Loss on sale of investments	9,134,183	2,398,483	6,626,908
Impairment loss on available-for-sale securities			1,290,590
Deferred income taxes	13,942,674	10,390,886	(688,619)
Stock based compensation expense related to employee stock options, employee stock purchases and restricted stock	14,197,557	10,652,196	9,084,891
Excess tax benefits from stock based compensation	(5,362,501)	(3,020,975)	(31,953)
Change in operating assets and liabilities:
Accounts receivable	(14,742,103)	(24,488,100)	(26,630,702)
Inventories	(88,024,582)	(47,119,734)	1,384,859
Prepaid expenses and other	(6,954,317)	(1,353,238)	12,232,402
Accounts payable	25,175,109	12,838,717	7,750,588
Accrued liabilities	1,794,548	177,332	1,337,105
Net cash provided by operating activities	141,668,665	128,133,686	110,654,296
CASH FLOWS FROM INVESTING ACTIVITIES:
Activity in available-for-sale securities: Sales proceeds	107,763,498	56,421,319	56,750,016
Activity in available-for-sale securities: Maturities and calls	104,375,000	36,000,000	36,250,000
Activity in available-for-sale securities: Purchases	(196,365,327)	(164,844,351)	(87,903,762)
Plant and equipment additions	(120,177,730)	(46,896,950)	(21,130,500)
Proceeds from sale of plant and equipment	179,212	504,977	26,060
Decrease (increase) in other assets	698,357	(5,771,488)	233,686
Net cash provided by (used for) investing activities	(103,526,990)	(124,586,493)	(15,774,500)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock from stock plan transactions	33,304,764	67,067,391	7,487,895
Cash dividends paid	(67,171,939)	(61,394,232)	(60,597,710)
Excess tax benefits from stock based compensation	5,362,501	3,020,975	31,953
Net cash used for financing activities	(28,504,674)	8,694,134	(53,077,862)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	9,637,001	12,241,327	41,801,934
CASH AND CASH EQUIVALENTS, Beginning of year	348,349,773	336,108,446	294,306,512
CASH AND CASH EQUIVALENTS, End of year	$ 357,986,774	$ 348,349,773	$ 336,108,446