CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 74,914,000	$ 16,773,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue and recognition of unbilled receivables	(63,942,000)	(29,266,000)
Depreciation	5,799,000	4,422,000
Amortization of intangibles	10,976,000	10,986,000
Change in excess inventory reserve	4,155,000	183,000
Amortization of premium and discount on investments, net	(3,150,000)	(2,329,000)
Stock-based compensation to employees	7,106,000	6,163,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	884,000	2,003,000
Deferred income tax (benefit) expense	(1,218,000)	19,312,000
Retirement plan expense	2,940,000	2,252,000
Decrease (increase) in assets:
Accounts receivable	(23,823,000)	16,772,000
Inventory	5,707,000	(19,778,000)
Other current assets	(2,816,000)	(9,058,000)
Other assets	(5,846,000)	(37,909,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(2,099,000)	(13,123,000)
Other current liabilities	6,736,000	(25,000)
Deferred revenue	68,213,000	64,423,000
Other liabilities	(657,000)	18,334,000
Net cash provided by operating activities	83,879,000	49,952,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(20,322,000)	(13,420,000)
Purchases of intangibles	(401,000)
Purchases of investments	(363,595,000)	(260,711,000)
Proceeds from sale of investments	437,800,000	211,847,000
Net cash provided by (used in) investing activities	53,482,000	(62,284,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	445,000	436,000
Repurchase of common stock	(649,000)	(477,000)
Payment of withholding taxes related to stock-based compensation to employees	(14,472,000)	(11,031,000)
Cash dividends paid	(9,430,000)	(5,659,000)
Net cash used in financing activities	(24,106,000)	(16,731,000)
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	113,255,000	(29,063,000)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	211,022,000	132,840,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 324,277,000	$ 103,777,000