INVESTMENTS: (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Amortized Cost
Amortized cost	$ 325,357		$ 328,677
Less amounts classified as cash and cash equivalents	(58,357)		(56,780)
Available-for-sale securities, amortized cost basis	267,000		271,897
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	65		39
Available for sale securities accumulated gross unrealized gain before tax less cash and cash equivalents	65		39
Unrealized losses	(232)		(275)
Available for sale securities accumulated gross unrealized loss before tax less cash and cash equivalents	(232)		(275)
Estimated Fair Value
Short term investments, fair value	325,190		328,441
Available-for-sale securities	266,833		271,661
Realized gains (losses) on the sale of marketable securities	900	$ (100)
Cash [Member]
Amortized Cost
Amortized cost	54,259		54,947
Estimated Fair Value
Short term investments, fair value	54,259		54,947
Money market funds [Member]
Amortized Cost
Amortized cost	4,098		1,833
Estimated Fair Value
Short term investments, fair value	4,098		1,833
Certificates of deposits [Member]
Amortized Cost
Amortized cost	79,147		78,643
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	0		0
Unrealized losses	0		0
Estimated Fair Value
Short term investments, fair value	79,147		78,643
U.S. Government and agency securities [Member]
Amortized Cost
Amortized cost	44,741		56,431
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	1		2
Unrealized losses	(106)		(86)
Estimated Fair Value
Short term investments, fair value	44,636		56,347
Commercial paper [Member]
Amortized Cost
Amortized cost	30,318		29,486
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	7		0
Unrealized losses	(9)		(3)
Estimated Fair Value
Short term investments, fair value	30,316		29,483
Corporate bonds [Member]
Amortized Cost
Amortized cost	89,131		94,292
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	51		37
Unrealized losses	(100)		(167)
Estimated Fair Value
Short term investments, fair value	89,082		94,162
Municipal bonds [Member]
Amortized Cost
Amortized cost	8,642		7,718
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	1		0
Unrealized losses	(8)		(12)
Estimated Fair Value
Short term investments, fair value	8,635		7,706
Foreign government bonds [Member]
Amortized Cost
Amortized cost	15,021		5,327
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	5		0
Unrealized losses	(9)		(7)
Estimated Fair Value
Short term investments, fair value	15,017		5,320
Cash and cash equivalents [Member]
Amortized Cost
Less amounts classified as cash and cash equivalents	(58,357)		(56,780)
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Unrealized gains	0		0
Unrealized losses	$ 0		$ 0

Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax Less Cash And Cash Equivalents

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Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax Less Cash And Cash Equivalents

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The item represents cash and cash equivalents. The cash equivalents are amounts of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operations.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents cash and cash equivalents and short-term investments.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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