Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 89,505,801	$ 104,280,411
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	26,295,146	28,098,804
(Gain) on disposal of assets	(151,910)	(43,338)
Loss on disposal of assets	54,279	122,296
(Gain) on sale of investments	(42,461)	(88,576)
Loss on sale of investments	5,487	0
Change in deferred income taxes	(1,589,855)	(1,233,853)
Stock-based compensation expense related to employee stock options, employee stock purchases and restricted stock	6,356,070	4,862,947
Change in operating assets and liabilities:
Accounts receivable, net	1,832,201	(30,728,497)
Inventories	(2,064,558)	(21,443)
Prepaid expenses and other	12,779,046	10,847,705
Accounts payable	2,545,274	(2,692,820)
Accrued liabilities, excluding dividends declared and short-term debt	15,755,950	20,436,582
Net cash provided by operating activities	151,280,470	133,840,218
Activity in available-for-sale securities:
Sales proceeds	3,124,008	17,139,689
Maturities and calls	19,720,000	3,000,000
Purchases	(48,606,718)	(18,475,158)
Plant and equipment additions	(15,574,443)	(16,844,301)
Proceeds from sale of plant and equipment	165,533	117,455
Decrease in other assets	(2,544,554)	164,215
Net cash (used for) investing activities	(43,716,174)	(14,898,100)
CASH FLOWS (USED FOR) FINANCING ACTIVITIES:
Proceeds from borrowings on Credit Agreement	75,000,000	0
Issuance of common stock from stock plan transactions	7,355,488	10,514,554
Cash dividends paid	(28,896,894)	(28,526,146)
Repurchases of common stock	(178,819,584)	(96,267,229)
Net cash (used for) financing activities	(125,360,990)	(114,278,821)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(17,796,694)	4,663,297
CASH AND CASH EQUIVALENTS, beginning of period	296,321,622	217,025,278
CASH AND CASH EQUIVALENTS, end of period	$ 278,524,928	$ 221,688,575