CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 138,337,000	$ 79,470,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(165,723,000)	(112,508,000)
Depreciation	14,471,000	11,147,000
Amortization of intangibles	16,490,000	16,474,000
Change in excess inventory reserve	2,058,000	808,000
Amortization of premium and discount on investments, net	(229,000)	(4,293,000)
Stock-based compensation to employees	22,846,000	19,807,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	1,052,000	1,133,000
Deferred income tax expense (benefit)	4,226,000	(2,242,000)
Retirement plan expense	6,676,000	4,242,000
Decrease (increase) in assets:
Accounts receivable	(13,974,000)	(38,898,000)
Inventory	(31,952,000)	(20,953,000)
Other current assets	(13,626,000)	(2,854,000)
Other assets	(33,540,000)	(8,721,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(3,311,000)	(19,633,000)
Other current liabilities	1,429,000	(806,000)
Deferred revenue	160,021,000	144,200,000
Other liabilities	31,933,000	9,454,000
Net cash provided by operating activities	134,326,000	75,827,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(29,496,000)	(19,213,000)
Purchases of intangibles	(394,000)	(25,000)
Purchases of investments	(272,340,000)	(604,153,000)
Proceeds from sale and maturity of investments	115,240,000	613,310,000
Net cash used in investing activities	(186,990,000)	(10,081,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	1,136,000	869,000
Payment of withholding taxes related to stock-based compensation to employees	(14,880,000)	(14,293,000)
Cash dividends paid	(28,447,000)	(21,329,000)
Net cash used in financing activities	(42,191,000)	(34,753,000)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(94,855,000)	30,993,000
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	630,012,000	131,627,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 535,157,000	$ 162,620,000