CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 49,970,000	$ 51,687,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(64,106,000)	(57,648,000)
Depreciation	5,627,000	4,263,000
Amortization of intangibles	5,498,000	5,488,000
Change in excess inventory reserve	84,000	667,000
Amortization of premium and discount on investments, net	(271,000)	(70,000)
Stock-based compensation to employees	6,085,000	5,200,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	430,000	330,000
Deferred income tax expense (benefit)	(1,380,000)	515,000
Retirement plan expense	1,359,000	2,228,000
Decrease (increase) in assets:
Accounts receivable	2,692,000	(9,066,000)
Inventory	(9,164,000)	(10,498,000)
Other current assets	(3,525,000)	5,400,000
Other assets	9,488,000	(7,133,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(4,261,000)	(21,136,000)
Other current liabilities	5,807,000	(666,000)
Deferred revenue	45,891,000	53,000,000
Other liabilities	(2,384,000)	6,935,000
Net cash provided by operating activities	52,608,000	29,496,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(10,751,000)	(9,938,000)
Purchases of intangibles	(12,000)	(298,000)
Purchases of investments	(24,915,000)	(4,220,000)
Proceeds from sale and maturity of investments	50,240,000	100,000,000
Net cash used in investing activities	14,562,000	85,544,000
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	403,000	348,000
Payment of withholding taxes related to stock-based compensation to employees	(7,896,000)	(9,634,000)
Cash dividends paid	(14,246,000)	(9,487,000)
Net cash used in financing activities	(21,739,000)	(18,773,000)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	45,431,000	96,267,000
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	311,993,000	630,012,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 357,424,000	$ 726,279,000