FAIR VALUE MEASUREMENTS: (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Financial assets measured at fair value
Transfers between Level 1 and Level 2	$ 0	$ 0
Fair Value, Measurements, Recurring Basis | Level 1
Financial assets measured at fair value
Financial assets	20,000,000
Fair Value, Measurements, Recurring Basis | Level 1 | Money market funds
Financial assets measured at fair value
Financial assets	20,000,000
Fair Value, Measurements, Recurring Basis | Level 2
Financial assets measured at fair value
Financial assets	264,924,000	312,441,000
Fair Value, Measurements, Recurring Basis | Level 2 | Certificates of deposit
Financial assets measured at fair value
Financial assets	67,769,000	90,431,000
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Government and agency securities
Financial assets measured at fair value
Financial assets	69,879,000	115,129,000
Fair Value, Measurements, Recurring Basis | Level 2 | Commercial paper
Financial assets measured at fair value
Financial assets	33,606,000	34,947,000
Fair Value, Measurements, Recurring Basis | Level 2 | Corporate bonds
Financial assets measured at fair value
Financial assets	92,274,000	61,462,000
Fair Value, Measurements, Recurring Basis | Level 2 | Foreign government bonds
Financial assets measured at fair value
Financial assets		7,530,000
Fair Value, Measurements, Recurring Basis | Level 2 | Derivative contracts
Financial assets measured at fair value
Financial assets	1,396,000	2,942,000
Fair Value, Measurements, Recurring Basis | Total
Financial assets measured at fair value
Financial assets	284,924,000	312,441,000
Fair Value, Measurements, Recurring Basis | Total | Money market funds
Financial assets measured at fair value
Financial assets	20,000,000
Fair Value, Measurements, Recurring Basis | Total | Certificates of deposit
Financial assets measured at fair value
Financial assets	67,769,000	90,431,000
Fair Value, Measurements, Recurring Basis | Total | U.S. Government and agency securities
Financial assets measured at fair value
Financial assets	69,879,000	115,129,000
Fair Value, Measurements, Recurring Basis | Total | Commercial paper
Financial assets measured at fair value
Financial assets	33,606,000	34,947,000
Fair Value, Measurements, Recurring Basis | Total | Corporate bonds
Financial assets measured at fair value
Financial assets	92,274,000	61,462,000
Fair Value, Measurements, Recurring Basis | Total | Foreign government bonds
Financial assets measured at fair value
Financial assets		7,530,000
Fair Value, Measurements, Recurring Basis | Total | Derivative contracts
Financial assets measured at fair value
Financial assets	$ 1,396,000	$ 2,942,000