Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Stock-based Compensation Expense by Award Type

The Company recognized the following stock-based compensation expense by award type and expense category line item during the years ended December 31 (in millions):

Award type	2017		2016		2015
Stock appreciation rights	$	5.6	$	5.6	$	5.7
Restricted stock units	72.6		40.4		39.8
Common stock equivalents	0.7		0.7		0.6
Total (1)	$	78.9	$	46.7	$	46.1

Schedule of Stock-based Compensation Expense by Expense Category

Expense category line item	2017		2016		2015
Cost of services and product development	$	25.8	$	21.9	$	20.6
Selling, general and administrative	35.5		24.8		25.5
Acquisition and integration charges (2)	17.6		—		—
Total (1)	$	78.9	$	46.7	$	46.1

(1) Includes charges of $22.9 million, $19.4 million and $20.1 million during 2017, 2016 and 2015, respectively, for awards to retirement-eligible employees. Those awards vest on an accelerated basis.

(2) These charges are primarily the result of the acceleration of the vesting of certain restricted stock units related to the CEB acquisition.

Schedule of Fair Value Assumptions of SARS

The fair value of a SARs award is determined on the date of grant using the Black-Scholes-Merton valuation model with the following weighted average assumptions for the years ended December 31:

	2017		2016		2015
Expected dividend yield (1)	—	%	—	%	—	%
Expected stock price volatility (2)	22	%	22	%	24	%
Risk-free interest rate (3)	1.8	%	1.1	%	1.5	%
Expected life in years (4)	4.53		4.39		4.41

(1) The expected dividend yield assumption was based on both the Company's historical and anticipated dividend payouts. Historically, the Company 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 was 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 estimate of the weighted average period of time the SARs are expected to be outstanding (that is, the period between the service inception date and the expected exercise date).

Stock Appreciation Rights (SARs)

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Summary of the Changes in SARS, RSUs, and CSEs Outstanding

The following table summarizes changes in SARs outstanding during the year ended December 31, 2017:  

	Stock Appreciation Rights ("SARs") (in millions)		Per Share Weighted Average Exercise Price		Per Share Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (Years)
Outstanding at December 31, 2016	1.3		$	66.22	$	15.77	4.40 years
Granted	0.3		99.07		22.02		6.10 years
Forfeited	(0.1	)	85.28		10.49		n/a
Exercised	(0.3	)	52.72		14.85		n/a
Outstanding at December 31, 2017 (1) (2)	1.2		$	76.73	$	17.35	4.28 years
Vested and exercisable at December 31, 2017 (2)	0.5		$	65.67	$	15.69	3.22 years

n/a = not applicable

(1) As of December 31, 2017, 0.7 million of the total SARs outstanding were unvested. The Company expects that substantially all of those unvested awards will vest in future periods.

(2) As of December 31, 2017, the total SARs outstanding had an intrinsic value of $55.0 million. On such date, SARs vested and exercisable had an intrinsic value of $30.2 million.

Restricted Stock Units (RSUs)

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Summary of the Changes in SARS, RSUs, and CSEs Outstanding

The following table summarizes the changes in RSUs outstanding during the year ended December 31, 2017:  

	Restricted Stock Units ("RSUs") (in millions)		Per Share Weighted Average Grant Date Fair Value
Outstanding at December 31, 2016	1.3		$	73.19
Granted (1) (2)	1.1		105.55
Vested and released	(0.8	)	79.60
Forfeited	(0.1	)	91.03
Outstanding at December 31, 2017 (3) (4)	1.5		$	91.47

(1) The 1.1 million of RSUs granted during 2017 consisted of 0.2 million of performance-based RSUs awarded to executives and 0.9 million of service-based RSUs awarded to executives, non-executive employees and non-management board members. The 0.2 million of performance-based RSUs represents the target amount of the grant for the year, which is tied to the increase

in heritage Gartner’s total contract value for 2017. Total contract value for this determination represents the value attributable to all of heritage Gartner’s subscription-related revenue contracts. The final number of performance-based RSUs awarded could range from 0% to 200% of the target amount. The actual increase in heritage Gartner’s contract value for 2017 as measured on December 31, 2017 yielded approximately 186% of the target amount. The incremental awards based on the actual achievement under the 2017 grant will be issued in 2018.

(2) Includes 0.6 million of RSUs awarded to employees that joined Gartner as a result of the CEB acquisition.

(3) The Company expects that substantially all of the RSUs outstanding will vest in future periods.

(4) As of December 31, 2017, the weighted average remaining contractual term of the RSUs outstanding was approximately 1.2 years.

Common Stock Equivalents (CSEs)

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Summary of the Changes in SARS, RSUs, and CSEs Outstanding

The following table summarizes the changes in CSEs outstanding during the year ended December 31, 2017:  

	Common Stock Equivalents ("CSEs")		Per Share Weighted Average Grant Date Fair Value
Outstanding at December 31, 2016	107,338		$	20.74
Granted	5,852		120.28
Converted to shares of Common Stock upon grant	(3,177	)	119.10
Outstanding at December 31, 2017	110,013		$	23.19