CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 51,687,000	$ 38,155,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(57,648,000)	(40,511,000)
Depreciation	4,263,000	3,615,000
Amortization of intangibles	5,488,000	5,490,000
Change in excess inventory reserve	667,000	611,000
Amortization of premium and discount on investments, net	(70,000)	(2,005,000)
Stock-based compensation to employees	5,200,000	5,735,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	330,000	254,000
Deferred income tax expense	515,000	940,000
Retirement plan expense	2,228,000	1,414,000
Decrease (increase) in assets:
Accounts receivable	(9,066,000)	(22,140,000)
Inventory	(10,498,000)	(10,726,000)
Other current assets	5,400,000	7,706,000
Other assets	(7,133,000)	(3,245,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(21,136,000)	(29,340,000)
Other current liabilities	(666,000)	3,114,000
Deferred revenue	53,000,000	43,685,000
Other liabilities	6,935,000	2,994,000
Net cash provided by operating activities	29,496,000	5,746,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(9,938,000)	(4,782,000)
Purchases of intangibles	(298,000)
Purchases of investments	(4,220,000)	(148,592,000)
Proceeds from sale and maturity of investments	100,000,000	250,400,000
Net cash provided by investing activities	85,544,000	97,026,000
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	348,000	259,000
Payment of withholding taxes related to stock-based compensation to employees	(9,634,000)	(4,816,000)
Cash dividends paid	(9,487,000)	(7,098,000)
Net cash used in financing activities	(18,773,000)	(11,655,000)
INCREASE IN CASH AND CASH EQUIVALENTS	96,267,000	91,117,000
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	630,012,000	131,627,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 726,279,000	$ 222,744,000