STOCK-BASED COMPENSATION

The Company's 1999 Omnibus Plan, as amended and restated effective March 2, 2017, (the "1999 Plan") is the primary stock compensation plan from which broad-based employee equity awards may be made. As of December 31, 2017, there were 2,129,531 shares of common stock available for future grant under the 1999 Plan. In addition, under plans assumed in connection with various acquisitions, there were 81,304 shares of common stock available for future grant as of December 31, 2017.

Stock-based compensation issued under the plans generally consists of restricted stock units, performance share units and, to a far lesser extent and typically only in the context of assuming grants in connection with acquisitions, stock options. Restricted stock units and performance share units generally vest over periods from 1 to 3 years. Stock options granted to employees generally have a term of 10 years. The Company issues new shares of common stock upon the vesting of restricted stock units and performance share units and the exercise of stock options. See Note 2 for the Company's accounting policy on stock-based compensation.

Stock-based compensation included in personnel expenses in the Consolidated Statements of Operations was approximately $260.9 million, $249.6 million and $247.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Stock-based compensation for the years ended December 31, 2017, 2016 and 2015 includes charges amounting to $10.6 million, $20.7 million and $22.6 million, respectively, representing the impact of adjusting the estimated probable outcome at the end of the performance period for outstanding unvested performance share units. Included in stock-based compensation are approximately $2.5 million, $2.6 million, and $2.6 million for the years ended December 31, 2017, 2016, and 2015, respectively, for restricted stock units awarded to non-employee directors. The related tax benefit for stock-based compensation is $46.0 million, $45.3 million and $52.9 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Restricted Stock Units and Performance Share Units

The following table summarizes the activity of restricted stock units and performance share units ("share-based awards") during the years ended December 31, 2015, 2016 and 2017:



Share-based Awards	Shares		Weighted-average Grant Date Fair Value

Unvested at December 31, 2014	570,315			$	912.26

Granted	198,141			$	1,226.41
Vested	(161,862	)		$	757.66
Performance Shares Adjustment	64,328			$	1,238.30
Forfeited/Canceled	(33,665	)		$	1,151.70
Unvested at December 31, 2015	637,257			$	1,070.10

Granted	202,740			$	1,314.93
Vested	(298,753	)		$	858.23
Performance Shares Adjustment	52,224			$	1,294.84
Forfeited/Canceled	(77,862	)		$	1,278.06
Unvested at December 31, 2016	515,606			$	1,287.88

Granted	174,507			$	1,740.78
Vested	(143,771	)		$	1,316.26
Performance Shares Adjustment	19,357			$	1,501.48
Forfeited/Canceled	(41,003	)		$	1,416.09
Unvested at December 31, 2017	524,696			$	1,431.88

Share-based awards granted by the Company during the years ended December 31, 2017, 2016 and 2015 had aggregate grant date fair values of approximately $303.8 million, $266.6 million and $243.0 million, respectively. Share-based awards that vested during the years ended December 31, 2017, 2016, and 2015 had grant date fair values of $189.2 million, $256.4 million and $122.6 million, respectively.

As of December 31, 2017, there was $349.7 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 1.8 years.

During the year ended December 31, 2017, the Company made broad-based grants of 100,614 restricted stock units that generally have a three-year vesting period, subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability. These share-based awards had a total grant date fair value of $175.6 million based on a weighted-average grant date fair value per share of $1,744.95.

In addition, during the year ended December 31, 2017, the Company granted 73,893 performance share units to executives and certain other employees. The performance share units had a total grant date fair value of $128.2 million based upon a weighted-average grant date fair value per share of $1,735.10. The performance share units are payable in shares of the Company's common stock upon vesting. Subject to certain exceptions for terminations other than for "cause," for "good reason" or on account of death or disability, recipients of these performance share units generally must continue their service through the requisite service period in order to receive any shares. Stock-based compensation related to performance share units reflects the estimated probable outcome at the end of the performance period. The actual number of shares to be issued on the vesting date will be determined upon completion of the performance period which generally ends December 31, 2019, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. As of December 31, 2017, the estimated number of probable shares to be issued is a total of 82,656 shares, net of performance share units forfeited and vested since the grant date. If the maximum performance thresholds are met at the end of the performance period, a maximum number of 139,190 total shares could be issued. If the minimum performance thresholds are not met, 56,338 shares would be issued at the end of the performance period.

2016 Performance Share Units

During the year ended December 31, 2016, the Company granted 85,735 performance share units with a grant date fair value of $111.7 million, based on a weighted-average grant date fair value per share of $1,302.25. The actual number of shares to be issued will be determined upon completion of the performance period which generally ends December 31, 2018, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances.

At December 31, 2017, there were 70,966 unvested 2016 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of December 31, 2017, the number of shares estimated to be issued pursuant to these performance share units at the end of the performance period is a total of 114,085 shares. If the maximum performance thresholds are met at the end of the performance period, a maximum of 159,876 total shares could be issued pursuant to these performance share units. If the minimum performance thresholds are not met, 42,663 shares would be issued at the end of the performance period.

2015 Performance Share Units

During the year ended December 31, 2015, the Company granted 107,623 performance share units with a grant date fair value of $133.2 million, based on a weighted-average grant date fair value per share of $1,237.53. The actual number of shares to be issued will be determined based upon completion of the performance period which ended December 31, 2017.

At December 31, 2017, there were 70,910 unvested 2015 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of December 31, 2017, the total number of shares expected to be issued pursuant to these performance share units during 2018 is 123,930 shares.

Stock Options

All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the years ended December 31, 2015, 2016 and 2017:



Employee Stock Options	Number of Shares		Weighted-average Exercise Price			Aggregate Intrinsic Value (in thousands)			Weighted-average Remaining Contractual Term (in years)
Balance, December 31, 2014	146,385			$	380.05		$	111,277	6.5
Assumed in acquisitions	1,422			$	230.37
Exercised	(52,697	)		$	355.85
Forfeited	(6,006	)		$	511.87
Balance, December 31, 2015	89,104			$	383.03		$	79,474	5.4
Exercised	(38,150	)		$	404.40
Forfeited	(1,971	)		$	241.65
Balance, December 31, 2016	48,983			$	372.07		$	53,587	4.4
Exercised	(17,359	)		$	294.45
Forfeited	(949	)		$	837.09
Balance, December 31, 2017	30,675			$	401.61		$	40,986	3.9
Vested and exercisable as of December 31, 2017	30,504			$	398.63		$	40,848	3.9
Vested and exercisable as of December 31, 2017 and expected to vest thereafter	30,675			$	401.61		$	40,986	3.9

The aggregate intrinsic value of employee stock options exercised during the years ended December 31, 2017, 2016 and 2015 was $26.0 million, $35.1 million and $46.3 million, respectively. During the years ended December 31, 2017, 2016 and 2015, stock options vested for 1,515, 12,180 and 38,689 shares, respectively, with an acquisition-date fair value of $0.9 million, $7.6 million and $24.4 million, respectively.

For the years ended December 31, 2017, 2016 and 2015, the Company recorded stock-based compensation expense related to employee stock options of $0.8 million, $6.8 million and $24.9 million, respectively. Employee stock options assumed during the year ended December 31, 2015 had a total acquisition-date fair value of $1.4 million based on a weighted-average acquisition date fair value of $1,015.81 per share. As of December 31, 2017, there was $0.1 million of total future compensation costs related to unvested employee stock options to be recognized over a weighted-average period of 0.3 years.