Weighted-Average Assumptions Used to Determine the Fair Value of the SARs Grants on the Date of the Grant Using the Black-Scholes-Merton Valuation Model (Detail) (Stock Appreciation Rights)	6 Months Ended
	Jun. 30, 2011 Year		Jun. 30, 2010 Year
Stock Appreciation Rights
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividend yield	0.00%	[1],[2]	0.00%	[1],[2]
Expected stock price volatility	38.00%	[1],[3]	40.00%	[1],[3]
Risk-free interest rate	2.20%	[1],[4]	2.40%	[1],[4]
Expected life in years	4.8	[1],[5]	4.8	[1],[5]

[1] The Company did not make any SARs grants during the three months ended June 30, 2011 or June 30, 2010.

[2] The dividend yield assumption is based on the history and expectation of the Company's dividend payouts. Historically, Gartner has not paid cash dividends on its Common Stock.

[3] The determination of expected stock price volatility was based on both historical Company Common Stock prices and implied volatility from publicly traded options in the Common Stock.

[4] The risk-free interest rate is based on the yield of a U.S. Treasury security with a maturity similar to the expected life of the award.

[5] The expected life represents a weighted-average estimate of the period of time the SARs are expected to be outstanding (that is, the period between the service inception date and the expected exercise date). The expected life in years is based on the "simplified" calculation permitted by SEC SAB No. 107. Under the simplified method, the expected life is calculated by taking the average of the vesting period plus the original contractual term and dividing by two.