CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 144,927	$ 138,337
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables, net	(201,529)	(165,723)
Depreciation	17,982	14,471
Amortization of intangibles	14,562	16,490
Change in excess inventory reserve	2,368	2,058
Amortization of premium and discount on investments, net	(3,469)	(229)
Stock-based compensation to employees	22,528	22,846
Stock-based compensation to Board of Directors and Scientific Advisory Board	1,121	1,052
Deferred income tax (benefit) expense	(7,876)	4,226
Retirement plan expense	3,998	6,676
Decrease (increase) in assets:
Accounts receivable	29,446	(13,974)
Inventory	(48,402)	(31,952)
Other current assets	(3,555)	(13,626)
Other assets	2,282	(33,540)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	7,217	(3,311)
Other current liabilities	(543)	(1,429)
Deferred revenue	132,961	160,021
Other liabilities	10,156	31,933
Net cash provided by operating activities	124,174	134,326
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(31,119)	(29,496)
Purchases of intangibles	(4,761)	(394)
Purchases of investments	(464,766)	(272,340)
Proceeds from sale and maturity of investments	302,872	115,240
Net cash used in investing activities	(197,774)	(186,990)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	1,247	1,136
Payment of withholding taxes related to stock-based compensation to employees	(9,150)	(14,880)
Cash dividends paid	(42,740)	(28,447)
Net cash used in financing activities	(50,643)	(42,191)
DECREASE IN CASH AND CASH EQUIVALENTS	(124,243)	(94,855)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	311,993	630,012
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 187,750	$ 535,157