FAIR VALUE (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Unobservable inputs assets (level 3) [Roll forward]
Auction rate securities variable rate debt instruments interest rate reset period	28 days
The minimum contractual maturities on the underlying securities involved in the auction rate securities (in years)	20 years
Temporary impairment of the auction rates security investments	$ (435,000)	$ (691,000)
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets measured at fair value	437,325,000	544,163,000
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total assets measured at fair value	405,597,000	160,275,000
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	5,043,000	310,482,000
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	11,178,000	56,255,000
Fair Value, Measurements, Recurring [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	15,507,000	17,151,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets measured at fair value	421,818,000	527,012,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	405,597,000	160,275,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	5,043,000	310,482,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	11,178,000	56,255,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Total assets measured at fair value	15,507,000	17,151,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	15,507,000	17,151,000
Auction Rate Securities [Member]
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	17,151,000	21,990,000
Decrease in unrealized loss included in accumulated other comprehensive loss	256,000	836,000
Settlements	(1,900,000)	(5,675,000)
Ending balance	15,507,000	$ 17,151,000
Par value of company held auction rate securities	$ 16,800,000
Discount rate (in percent)	4.70%	4.10%
Temporary impairment of the auction rates security investments	$ (435,000)