Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 151,741,878		$ 145,292,817
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42,471,227		39,592,545
Gain on disposal of assets	(18,052)		(35,000)
Loss on disposal of assets	250,247		374,925
Gain on sale of investments	(4,835,125)		(12,213,259)
Loss on sale of investments	307,110		647,520
Deferred income taxes	(2,472,624)		667,802
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	11,224,538		10,147,262
Excess tax benefits from stock-based compensation	(1,629,160)		(1,403,740)
Change in operating assets and liabilities:
Accounts receivable, net	(28,050,976)		(35,234,410)
Inventories	(9,014,610)		(5,137,710)
Prepaid expenses and other	11,612,976		(7,809,607)
Accounts payable	(1,520,783)		(689,646)
Accrued liabilities, excluding dividends declared	21,821,075		7,906,087
Net cash provided by operating activities	191,887,721		142,105,586
Activity in available-for-sale securities:
Sales proceeds	13,805,507		55,370,528
Purchases	(12,939,815)		(52,943,104)
Plant and equipment additions	(33,589,833)		(30,248,002)
Proceeds from sale of plant and equipment	4		35,005
(Increase) in other assets	(1,084,292)		(683,656)
Net cash (used for) investing activities	(33,808,429)		(28,469,229)
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Repayment of long-term debt	(3,750,000)		(3,750,000)
Issuance of common stock from stock plan transactions	13,809,419		11,576,970
Cash dividends paid	(47,193,926)		(40,808,322)
Repurchases of common stock	(50,107,196)		0
Excess tax benefits from stock-based compensation	1,629,160		1,403,740
Net cash (used for) financing activities	(85,612,543)		(31,577,612)
NET INCREASE IN CASH AND CASH EQUIVALENTS	72,466,749		82,058,745
CASH AND CASH EQUIVALENTS, beginning of period	497,429,804	[1]	309,591,724
CASH AND CASH EQUIVALENTS, end of period	$ 569,896,553		$ 391,650,469

[1] Note: The condensed consolidated balance sheet at December 31, 2014 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.