SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	9 Months Ended
	Sep. 30, 2013 item	Sep. 30, 2012	Dec. 31, 2012
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Restricted cash	$ 0		$ 0
Number of objectives of the entity's investment strategy	2
Realized losses	0	0
Realized gains	5,100	4,200
Minimum contractual term of certain current investments which can be liquidated	1 year
Available-for-sale securities
Amortized Cost	138,013,000		94,698,000
Gains in Accumulated Other Comprehensive Income	118,000		78,000
Estimated Fair Value	138,131,000		94,776,000
U.S. government agency securities
Available-for-sale securities
Amortized Cost	44,477,000		44,270,000
Gains in Accumulated Other Comprehensive Income	56,000		38,000
Estimated Fair Value	44,533,000		44,308,000
Corporate bonds
Available-for-sale securities
Amortized Cost	80,973,000		43,303,000
Gains in Accumulated Other Comprehensive Income	52,000		27,000
Estimated Fair Value	81,025,000		43,330,000
Certificates of deposit
Available-for-sale securities
Amortized Cost	7,565,000		5,926,000
Gains in Accumulated Other Comprehensive Income	9,000		13,000
Estimated Fair Value	7,574,000		5,939,000
Commercial paper
Available-for-sale securities
Amortized Cost	4,998,000		1,199,000
Gains in Accumulated Other Comprehensive Income	1,000
Estimated Fair Value	$ 4,999,000		$ 1,199,000