CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 91,472,000	$ 92,228,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(125,196,000)	(110,993,000)
Depreciation	11,529,000	9,229,000
Amortization of intangibles	11,000,000	10,985,000
Change in excess inventory reserve	688,000	1,117,000
Amortization of premium and discount on investments, net	(1,027,000)	(128,000)
Stock-based compensation to employees	14,282,000	14,624,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	774,000	704,000
Deferred income tax expense (benefit)	(2,282,000)	1,458,000
Retirement plan expense	2,718,000	4,457,000
Decrease (increase) in assets:
Accounts receivable	32,706,000	(17,368,000)
Inventory	(32,163,000)	(14,179,000)
Other current assets	(13,030,000)	(5,712,000)
Other assets	7,522,000	(15,005,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(7,126,000)	(17,036,000)
Other current liabilities	(3,343,000)	(2,536,000)
Deferred revenue	92,976,000	92,816,000
Other liabilities	4,630,000	14,455,000
Net cash provided by operating activities	86,130,000	59,116,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(21,336,000)	(20,668,000)
Purchases of intangibles	(12,000)	(394,000)
Purchases of investments	(287,919,000)	(193,951,000)
Proceeds from sale and maturity of investments	161,530,000	100,000,000
Net cash used in investing activities	(147,737,000)	(115,013,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	847,000	787,000
Payment of withholding taxes related to stock-based compensation to employees	(8,844,000)	(13,018,000)
Cash dividends paid	(28,493,000)	(18,970,000)
Net cash used in financing activities	(36,490,000)	(31,201,000)
DECREASE IN CASH AND CASH EQUIVALENTS	(98,097,000)	(87,098,000)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	311,993,000	630,012,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 213,896,000	$ 542,914,000