Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 97,556,741		$ 80,279,994
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,181,854		22,839,030
Gain on disposal of assets	(146,261)		(10,900)
Loss on disposal of assets	359,959		577,916
Gain on sale of investments	(274,844)		(1,498,949)
Loss on sale of investments	21,431		1,961,673
Deferred income taxes	5,718,363		(2,403,818)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	4,422,996		4,974,453
Change in operating assets and liabilities:
Accounts receivable, net	(37,866,173)		(28,020,070)
Inventories	(7,776,814)		(13,929,365)
Prepaid expenses and other	18,857,501		23,521,639
Accounts payable	(2,249,350)		13,065,406
Accrued liabilities, excluding dividends declared and short-term debt	27,385,768		50,511,519
Net cash provided by operating activities	131,191,171		151,868,528
Activity in available-for-sale securities:
Sales proceeds	1,316,280		43,417,073
Maturities and calls	6,100,000		0
Purchases	(16,225,018)		(25,154,245)
Plant and equipment additions	(27,119,993)		(20,329,035)
Proceeds from sale of plant and equipment	15,001		516,667
(Increase) Decrease in other assets	(588,361)		135,904
Net cash used for investing activities	(36,502,091)		(1,413,636)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Repayment of long-term debt	(41,875,000)		(16,875,000)
Issuance of common stock from stock plan transactions	17,237,232		10,678,450
Cash dividends paid	(25,896,377)		(24,759,481)
Repurchases of common stock	(30,986,385)		(44,585,668)
Net cash used for financing activities	(81,520,530)		(75,541,699)
NET INCREASE IN CASH AND CASH EQUIVALENTS	13,168,550		74,913,193
CASH AND CASH EQUIVALENTS, beginning of period	546,477,075	[1]	551,557,527
CASH AND CASH EQUIVALENTS, end of period	$ 559,645,625		$ 626,470,720

[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.