Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 222,929,949	$ 168,586,840	$ 164,668,228
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,854,155	50,179,823	42,634,684
Gain on disposal of assets	(54,520)	(419,382)	0
Loss on disposal of assets	2,162,610	952,190	992,876
Gain on sale of investments	(19,012,429)	(9,584,288)	(15,787,691)
Loss on sale of investments	882,918	1,216,027	9,134,183
Deferred income taxes	(7,726,800)	843,484	13,942,674
Stock based compensation expense related to employee stock options, employee stock purchases and restricted stock	17,427,233	16,433,837	14,197,557
Excess tax benefits from stock based compensation	(4,445,064)	(815,651)	(5,362,501)
Change in operating assets and liabilities:
Accounts receivable	(22,347,450)	810,022	(14,742,103)
Inventories	39,856,102	28,823,046	(88,024,582)
Prepaid expenses and other	(2,374,913)	14,868,742	(6,954,317)
Accounts payable	13,310,319	(22,270,571)	25,175,109
Accrued liabilities	13,876,720	8,221,935	1,794,548
Net cash provided by operating activities	317,338,830	257,846,054	141,668,665
Activity in available-for-sale securities:
Sales proceeds	82,862,644	38,831,234	107,763,498
Maturities and calls	98,142,408	75,652,000	104,375,000
Purchases	(60,543,153)	(112,545,415)	(196,365,327)
Plant and equipment additions	(55,380,457)	(117,474,449)	(120,177,730)
Proceeds from sale of plant and equipment	386,399	1,064,614	179,212
Acquisition of businesses, net of cash acquired	(698,150,900)	0	0
Decrease (increase) in other assets	(573,560)	(17,602,228)	698,357
Net cash provided by (used for) investing activities	(633,256,619)	(132,074,244)	(103,526,990)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from borrowings on Credit Agreement	275,000,000	0	0
Repayment of long-term debt	(1,875,000)	0	0
Deferred financing costs	(956,441)	0	0
Issuance of common stock from stock plan transactions	38,377,571	12,208,881	33,304,764
Cash dividends paid	(79,160,345)	(73,387,727)	(67,171,939)
Repurchases of common stock	0	(33,716,725)	0
Excess tax benefits from stock based compensation	4,445,064	815,651	5,362,501
Net cash provided by (used for) financing activities	235,830,849	(94,079,920)	(28,504,674)
NET INCREASE IN CASH AND CASH EQUIVALENTS	(80,086,940)	31,691,890	9,637,001
CASH AND CASH EQUIVALENTS, Beginning of year	389,678,664	357,986,774	348,349,773
CASH AND CASH EQUIVALENTS, End of year	$ 309,591,724	$ 389,678,664	$ 357,986,774