Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 186,092,688		$ 166,765,236
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	50,428,320		45,789,787
Gain on disposal of assets	(83,667)		(10,900)
Loss on disposal of assets	286,318		705,381
Gain on sale of investments	(876,496)		(1,657,211)
Loss on sale of investments	37,718		2,144,668
Deferred income taxes	7,008,364		(402,154)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	9,114,708		9,777,427
Change in operating assets and liabilities:
Accounts receivable, net	(17,658,594)		(23,473,550)
Inventories	(7,228,785)		(1,531,186)
Prepaid expenses and other	16,812,179		19,882,083
Accounts payable	2,957,299		15,469,383
Accrued liabilities, excluding dividends declared and short-term debt	16,667,667		21,670,990
Net cash provided by operating activities	263,557,719		255,129,954
Activity in available-for-sale securities:
Sales proceeds	2,179,926		45,982,921
Maturities and calls	12,100,000		0
Purchases	(17,216,593)		(165,496,238)
Plant and equipment additions	(56,218,870)		(54,832,532)
Proceeds from sale of plant and equipment	89,701		516,667
Decrease (Increase) in other assets	1,783,574		(2,287,732)
Net cash used for investing activities	(57,282,262)		(176,116,914)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of long-term debt	(68,750,000)		(18,750,000)
Issuance of common stock from stock plan transactions	21,929,900		29,282,769
Cash dividends paid	(51,796,194)		(49,334,501)
Repurchases of common stock	(73,556,886)		(92,274,871)
Net cash used for financing activities	(172,173,180)		(131,076,603)
NET INCREASE IN CASH AND CASH EQUIVALENTS	34,102,277		(52,063,563)
CASH AND CASH EQUIVALENTS, beginning of period	546,477,075	[1]	551,557,527
CASH AND CASH EQUIVALENTS, end of period	$ 580,579,352		$ 499,493,964

[1] Note: The condensed consolidated balance sheet at December 31, 2016 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.