CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 38,155,000	$ 31,474,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(40,511,000)	(26,976,000)
Depreciation	3,615,000	2,758,000
Amortization of intangibles	5,490,000	5,486,000
Change in excess inventory reserve	611,000	224,000
Amortization of premium and discount on investments, net	(2,005,000)	(1,741,000)
Stock-based compensation to employees	5,735,000	3,610,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	254,000	516,000
Deferred income tax expense (benefit)	940,000	(592,000)
Retirement plan expense	1,414,000	1,501,000
Decrease (increase) in assets:
Accounts receivable	(22,140,000)	(8,995,000)
Inventory	(10,726,000)	1,735,000
Other current assets	7,706,000	177,000
Other assets	(3,245,000)	(2,966,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(29,340,000)	(12,117,000)
Other current liabilities	3,114,000	3,744,000
Deferred revenue	43,685,000	33,080,000
Other liabilities	2,994,000	3,132,000
Net cash provided by operating activities	5,746,000	34,050,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(4,782,000)	(13,283,000)
Purchases of intangibles		(401,000)
Purchases of investments	(148,592,000)	(165,471,000)
Proceeds from sale of investments	250,400,000	170,050,000
Net cash provided by (used in) investing activities	97,026,000	(9,105,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	259,000	204,000
Repurchase of common stock		(649,000)
Payment of withholding taxes related to stock-based compensation to employees	(4,816,000)	(5,757,000)
Cash dividends paid	(7,098,000)	(4,717,000)
Net cash used in financing activities	(11,655,000)	(10,919,000)
INCREASE IN CASH AND CASH EQUIVALENTS	91,117,000	14,026,000
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	131,627,000	211,022,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 222,744,000	$ 225,048,000