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FAIR VALUE (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended																																													9 Months Ended	12 Months Ended									9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Cash [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Cash [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Money Market Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Money Market Funds [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Government-Sponsored Enterprise Obligations [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Auction Rate Securities [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Cash [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Cash [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Money Market Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Money Market Funds [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Government-Sponsored Enterprise Obligations [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member] Auction Rate Securities [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Cash [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Cash [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Money Market Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Money Market Funds [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Government-Sponsored Enterprise Obligations [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Auction Rate Securities [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Cash [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Cash [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Money Market Funds [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Money Market Funds [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Commercial Paper [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Government-Sponsored Enterprise Obligations [Member]	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Auction Rate Securities [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member] Auction Rate Securities [Member]	Sep. 30, 2013 Auction Rate Securities [Member]	Dec. 31, 2012 Auction Rate Securities [Member]	Dec. 31, 2011 Auction Rate Securities [Member]	Dec. 31, 2010 Auction Rate Securities [Member]	Dec. 31, 2009 Auction Rate Securities [Member]	Dec. 31, 2008 Auction Rate Securities [Member]	Sep. 30, 2013 LandsofAmerica [Member]	Mar. 28, 2013 LandsofAmerica [Member]	Sep. 30, 2013 Reaction Web [Member]	Mar. 28, 2013 Reaction Web [Member]	Sep. 30, 2013 LoopNet [Member]	Dec. 31, 2012 LoopNet [Member]
Assets:
Total assets measured at fair value						$ 244,613,000	$ 177,726,000	$ 136,909,000	$ 135,232,000	$ 32,338,000	$ 20,775,000	$ 53,691,000	$ 20,000	$ 37,000	$ 21,675,000	$ 21,662,000	$ 222,938,000	$ 156,027,000	$ 136,909,000	$ 135,232,000	$ 32,338,000	$ 20,775,000	$ 53,691,000	$ 20,000	$ 0	$ 0	$ 0	$ 0	$ 37,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 37,000	$ 0	$ 0	$ 21,675,000	$ 21,662,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 21,675,000	$ 21,662,000
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	21,675,000	24,976,000	21,662,000	24,584,000	24,584,000																																													21,662,000	24,584,000	29,189,000	29,724,000	29,340,000	53,975,000
Auction rate securities upon acquisition	0	0	0	442,000																																															442,000
Change in unrealized gain (loss) included in accumulated other comprehensive loss	0	735,000	63,000	735,000																																														63,000	836,000	245,000	40,000	684,000	(3,710,000)
Settlements	0	(4,150,000)	(50,000)	(4,200,000)																																														(50,000)	(4,200,000)	(4,850,000)	(575,000)	(300,000)	(20,925,000)
Ending balance	21,675,000	21,561,000	21,675,000	21,561,000	21,662,000																																													21,675,000	21,662,000	24,584,000	29,189,000	29,724,000	29,340,000
Auction rate securities variable rate debt instruments interest rate reset period			28 days
The minimum contractual maturities on underlying securities involved in auction rate securities			20 years
Par value of company held auction rate securities	24,300,000		24,300,000
Temporary impairment of the auction rates security investments	(1,842,000)		(1,842,000)		(1,905,000)
Liabilities:
Deferred consideration						1,208,000	2,304,000										0	0										0	0										1,208,000	2,304,000
Unobservable inputs liabilities (level 3) [Roll forward]
Beginning balance	1,146,000	2,072,000	2,304,000	0	0
Deferred consideration upon acquisition	0	0	0	2,011,000	2,011,000
Accretion	62,000	113,000	248,000	174,000	293,000
Payments	0	0	(1,344,000)	0
Ending balance	1,208,000	2,185,000	1,208,000	2,185,000	2,304,000
Business acquisition deferred consideration potential cash payment (undiscounted)																																																								1,000,000		344,000
Business acquisition deferred consideration cash payment																																																									$ 1,000,000		$ 344,000
Discount rate (in percent)			5.20%		5.10%																																																							23.50%	23.50%

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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