STOCK-BASED EMPLOYEE COMPENSATION

Stock-based compensation expense included in personnel expenses in the Unaudited Consolidated Statements of Operations was approximately $55.0 million and $60.2 million for the three months ended June 30, 2016 and 2015, respectively, and $121.0 million and $114.2 million for the six months ended June 30, 2016 and 2015, respectively.

Stock-based compensation is recognized in the financial statements based upon fair value. Fair value is recognized as expense on a straight-line basis, net of estimated forfeitures, over the employee's requisite service period. The fair value of performance share units and restricted stock units is determined based on the number of units granted and the quoted price of the Company's common stock as of the grant date. Stock-based compensation related to performance share units reflects the estimated probable outcome at the end of the performance period. The fair value of employee stock options assumed in acquisitions was determined using the Black-Scholes model and the market value of the Company's common stock at the respective acquisition dates.

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 six months ended June 30, 2016:



Share-Based Awards	Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2015	637,257			$	1,070.10
Granted	184,591			$	1,299.27
Vested	(279,453	)		$	830.50
Performance Share Units Adjustment	3,088			$	1,267.85
Forfeited	(59,161	)		$	1,275.12
Unvested at June 30, 2016	486,322			$	1,278.90

As of June 30, 2016, there was $380.8 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 2.1 years.

During the six months ended June 30, 2016, the Company made broad-based grants of 98,856 restricted stock units that generally vest after three years, 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 $128.2 million based on a weighted-average grant date fair value per share of $1,296.68.

In addition, during the six months ended June 30, 2016, the Company granted 85,735 performance share units to executives and certain other employees. The performance share units had a total grant date fair value of $111.6 million based upon a weighted-average grant date fair value per share of $1,302.25. 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 ends December 31, 2018, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. As of June 30, 2016, the estimated number of probable shares to be issued is a total of 80,671 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 181,726 total shares could be issued. If the minimum performance thresholds are not met, 47,626 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 upon completion of the performance period which generally ends December 31, 2017.

At June 30, 2016, there were 79,410 unvested 2015 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of June 30, 2016, 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 130,723 shares. If the maximum performance thresholds are met at the end of the performance period, a maximum of 197,115 total shares could be issued pursuant to these performance share units. If the minimum performance thresholds are not met, 46,327 shares would be issued at the end of the performance period.

2014 Performance Share Units

During the year ended December 31, 2014, the Company granted 72,277 performance share units with a grant date fair value of $96.1 million, based on a weighted-average grant date fair value per share of $1,329.11. The actual number of shares to be issued will be determined upon completion of the performance period which generally ends December 31, 2016.

At June 30, 2016, there were 45,198 unvested 2014 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of June 30, 2016, 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 72,552 shares. If the maximum performance thresholds are met at the end of the performance period, a maximum of 91,160 total shares could be issued pursuant to these performance share units. If the minimum performance thresholds are not met, 35,467 shares would be issued at the end of the performance period.

Stock Options

The following table summarizes the activity for stock options during the six months ended June 30, 2016:



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, 2015	89,104			$	383.03		$	79,474	5.4
Exercised	(25,962	)		$	374.66
Forfeited	(1,410	)		$	253.97
Balance, June 30, 2016	61,732			$	389.49		$	53,023	5.1
Vested and exercisable as of June 30, 2016	56,002			$	364.94		$	49,476	4.9
Vested and exercisable as of June 30, 2016 and expected to vest thereafter, net of estimated forfeitures	61,542			$	389.69		$	52,847	5.1

The aggregate intrinsic value of employee stock options assumed in acquisitions that were exercised during the six months ended June 30, 2016 was $23.1 million compared to $26.4 million for the six months ended June 30, 2015. During the six months ended June 30, 2016, stock options assumed in acquisitions vested for 9,387 shares of common stock with an acquisition-date fair value of $5.9 million, compared to 22,352 shares of common stock vested for stock options assumed in acquisitions with an acquisition-date fair value of $15.1 million for the six months ended June 30, 2015.

For the three and six months ended June 30, 2016, the Company recorded stock-based compensation expense related to employee stock options of $2.4 million and $5.3 million, respectively, compared to $7.6 million and $15.0 million for the three and six months ended June 30, 2015, respectively. As of June 30, 2016, there was $3.3 million of total future compensation costs related to unvested employee stock options to be recognized over a weighted-average period of 1.1 years.