INTANGIBLES AND OTHER ASSETS (Details) (USD $) In Thousands, unless otherwise specified			9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended			0 Months Ended
Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Capitalized Product Development Costs [Member]	Dec. 31, 2012 Capitalized Product Development Costs [Member]	Sep. 30, 2013 Building Photography [Member]	Dec. 31, 2012 Building Photography [Member]	Sep. 30, 2013 Acquired Database Technology [Member]	Dec. 31, 2012 Acquired Database Technology [Member]	Sep. 30, 2013 Acquired Customer Base [Member]	Dec. 31, 2012 Acquired Customer Base [Member]	Sep. 30, 2013 Acquired Trade Names and Other [Member]	Dec. 31, 2012 Acquired Trade Names and Other [Member]	Apr. 30, 2012 LoopNet [Member]	Apr. 30, 2012 LoopNet [Member] Acquired Database Technology [Member]	Apr. 30, 2012 LoopNet [Member] Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business acquisition, purchase price allocation, Intangible assets not amortizable													$ 48,700
Finite-lived intangible assets, gross			2,140	2,140	13,566	12,474	77,325	77,328	130,662	130,683	59,249	59,255
Finite-lived intangible assets, accumulated amortization			(1,981)	(1,838)	(11,830)	(11,639)	(38,284)	(29,673)	(70,968)	(59,218)	(9,079)	(8,880)
Finite-lived intangible assets, net	$ 150,800	$ 170,632	$ 159	$ 302	$ 1,736	$ 835	$ 39,041	$ 47,655	$ 59,694	$ 71,465	$ 50,170	$ 50,375
Weighted-average amortization period (in years}			4 years		5 years		5 years		10 years		7 years			5 years	10 years

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Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

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- Definition

Amount of assets, excluding financial assets and goodwill, that lack physical substance, having a projected indefinite period of benefit, acquired at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

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- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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