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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Marketable Securities (Details) | 3 Months Ended |
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Mar. 31, 2016 USD ($) item | Mar. 31, 2015 USD ($) | Dec. 31, 2015 USD ($)
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES |  |  |
Number of objectives of the entity's investment strategy | item | 2 |  |
Realized gains | $ 3,300 | $ 3,000 |
Minimum contractual term of certain current investments which can be liquidated | 1 year |  |
Available-for-sale securities |  |  |
Amortized Cost | $ 210,412,000 |  | $ 266,188,000
Gains in Accumulated Other Comprehensive Income | 115,000 |  | 2,000
Losses in Accumulated Other Comprehensive Income | (86,000) |  | (446,000)
Estimated Fair Value | 210,441,000 |  | 265,744,000
Realized losses | 0 | $ 0 |
Corporate bonds |  |  |
Available-for-sale securities |  |  |
Amortized Cost | 132,854,000 |  | 179,471,000
Gains in Accumulated Other Comprehensive Income | 93,000 |  | 2,000
Losses in Accumulated Other Comprehensive Income | (41,000) |  | (262,000)
Estimated Fair Value | 132,906,000 |  | 179,211,000
Asset backed securities |  |  |
Available-for-sale securities |  |  |
Amortized Cost | 62,380,000 |  | 77,661,000
Gains in Accumulated Other Comprehensive Income | 12,000 |  |
Losses in Accumulated Other Comprehensive Income | (44,000) |  | (166,000)
Estimated Fair Value | 62,348,000 |  | 77,495,000
U.S. government agency securities |  |  |
Available-for-sale securities |  |  |
Amortized Cost | 7,057,000 |  | 7,057,000
Gains in Accumulated Other Comprehensive Income | 8,000 |  |
Losses in Accumulated Other Comprehensive Income |  |  | (18,000)
Estimated Fair Value | 7,065,000 |  | 7,039,000
Certificates of deposit |  |  |
Available-for-sale securities |  |  |
Amortized Cost | 5,500,000 |  | 1,999,000
Gains in Accumulated Other Comprehensive Income | 2,000 |  |
Estimated Fair Value | 5,502,000 |  | $ 1,999,000
Commercial paper |  |  |
Available-for-sale securities |  |  |
Amortized Cost | 2,621,000 |  |
Losses in Accumulated Other Comprehensive Income | (1,000) |  |
Estimated Fair Value | $ 2,620,000 |  |

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- Definition Represents the minimum contractual term of certain current investments which the company has the ability and intent, if necessary, to liquidate in order to support its current operations. + References No definition available. + Details
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- Definition Represents the number of objectives of the entity's investment strategies. + References No definition available. + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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