FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Fair value disclosure
Cash and cash equivalents	$ 159,382,000	$ 105,354,000	$ 107,611,000	$ 90,702,000
Short-term investments	43,858,000	35,906,000
Restricted cash, cash equivalents, and short-term investments	1,385,000	1,902,000
Concentrations of Credit Risk of Financial Instruments
Cash, cash equivalents, and certificates of deposit which are not FDIC-insured	58,000,000	49,400,000
Fair value disclosure
Fair value disclosure
Cash and cash equivalents	159,382,000	105,354,000
Fair value disclosure | Cash deposits
Fair value disclosure
Cash and cash equivalents	108,473,000	63,547,000
Restricted cash, cash equivalents, and short-term investments	1,385,000	1,902,000
Fair value disclosure | Variable rate demand notes
Fair value disclosure
Cash and cash equivalents	16,307,000	29,706,000
Fair value disclosure | Money market funds
Fair value disclosure
Cash and cash equivalents	34,602,000	12,101,000
Fair value disclosure | Certificates of deposit
Fair value disclosure
Short-term investments	$ 43,858,000	$ 35,906,000