CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 111,876,000	$ 39,591,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(101,079,000)	(52,325,000)
Depreciation	8,958,000	6,094,000
Amortization of intangibles	16,469,000	16,479,000
Change in excess inventory reserve	4,155,000	1,045,000
Amortization of premium and discount on investments, net	(4,528,000)	(4,191,000)
Stock-based compensation to employees	10,697,000	9,697,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	1,126,000	3,234,000
Deferred income tax (benefit) expense	(2,633,000)	15,820,000
Retirement plan expense	4,379,000	3,378,000
Decrease (increase) in assets:
Accounts receivable	(22,645,000)	9,148,000
Inventory	8,074,000	(33,811,000)
Other current assets	(4,602,000)	(116,000)
Other assets	(10,259,000)	(37,769,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(1,827,000)	439,000
Other current liabilities	5,587,000	(34,000)
Deferred revenue	113,849,000	99,940,000
Other liabilities	149,000	18,337,000
Net cash provided by operating activities	137,746,000	94,956,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(25,317,000)	(20,925,000)
Purchases of intangibles	(401,000)
Purchases of investments	(648,006,000)	(500,985,000)
Proceeds from sale of investments	590,550,000	415,697,000
Net cash used in investing activities	(83,174,000)	(106,213,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	658,000	616,000
Repurchase of common stock	(649,000)	(477,000)
Payment of withholding taxes related to stock-based compensation to employees	(15,920,000)	(11,598,000)
Cash dividends paid	(14,142,000)	(8,486,000)
Net cash used in financing activities	(30,053,000)	(19,945,000)
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	24,519,000	(31,202,000)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	211,022,000	132,840,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 235,541,000	$ 101,638,000