Stock-Based Compensation (Detail) - Weighted-Average Assumptions Used To Determine Fair Value Of SARs Grants On Date Of Grant Using Black-Scholes-Merton Valuation Model (Stock appreciation rights (SARs))	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Stock appreciation rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected dividend yield	0.00%	[1]	0.00%	[1]
Expected stock price volatility	35.00%	[2]	40.00%	[2]
Risk-free interest rate	0.80%	[3]	0.80%	[3]
Expected life in years	4 years 6 months	[4]	4 years 219 days	[4]

[1] 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.

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

[3] 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.

[4] The expected life represents the Company’s weighted-average estimate of the period of time the SARs are expected to be outstanding (defined as the period between the service inception date and the expected exercise date), which is based on historical exercise data.