STOCK-BASED EMPLOYEE COMPENSATION

Stock-based compensation expense included in personnel expenses in the Unaudited Consolidated Statements of Operations was approximately $66.4 million and $54.1 million for the three months ended September 30, 2017 and 2016, respectively, and $192.2 million and $175.1 million for the nine months ended September 30, 2017 and 2016, respectively.

Stock-based compensation expense is recognized in the financial statements based upon fair value. Fair value is recognized as expense on a straight-line basis 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 expense 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 nine months ended September 30, 2017:



Share-Based Awards	Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2016	515,606			$	1,287.88
Granted	166,957			$	1,742.75
Vested	(136,344	)		$	1,314.49
Performance Share Units Adjustment	6,702			$	1,274.19
Forfeited	(32,081	)		$	1,402.11
Unvested at September 30, 2017	520,840			$	1,420.00

As of September 30, 2017, there was $395.2 million of total future compensation cost related to unvested share-based awards to be recognized over a weighted-average period of 1.9 years.

During the nine months ended September 30, 2017, the Company made broad-based grants of 93,064 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 $162.8 million based on a weighted-average grant date fair value per share of $1,748.82.

In addition, during the nine months ended September 30, 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 ends December 31, 2019, assuming there is no accelerated vesting for, among other things, a termination of employment under certain circumstances. As of September 30, 2017, the estimated number of probable shares to be issued is a total of 70,718 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 141,436 total shares could be issued. If the minimum performance thresholds are not met, 57,461 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.

At September 30, 2017, there were 71,464 unvested 2016 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of September 30, 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 115,576 shares. If the maximum thresholds are met at the end of the performance period, a maximum of 161,006 total shares could be issued pursuant to these performance share units. If the minimum performance thresholds are not met, 43,027 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 September 30, 2017, there were 71,475 unvested 2015 performance share units outstanding, net of performance share units that were forfeited or vested since the grant date. As of September 30, 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 124,617 shares. If the maximum thresholds are met at the end of the performance period, a maximum of 177,351 total shares could be issued pursuant to these performance share units. If the minimum performance thresholds are not met, 41,480 shares would be issued at the end of the performance period.

Stock Options

All outstanding employee stock options were assumed in acquisitions. The following table summarizes the activity for stock options during the nine months ended September 30, 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, 2016	48,983			$	372.07		$	53,587	4.4
Exercised	(14,236	)		$	301.68
Forfeited	(948	)		$	837.90
Balance, September 30, 2017	33,799			$	388.65		$	48,744	4.0
Vested and exercisable as of September 30, 2017	33,400			$	383.56		$	48,338	4.0
Vested and exercisable as of September 30, 2017 and expected to vest thereafter	33,799			$	388.65		$	48,744	4.0

The aggregate intrinsic value of employee stock options that were exercised during the nine months ended September 30, 2017 and 2016 was $21.4 million and $31.8 million, respectively. During the nine months ended September 30, 2017 and 2016, stock options vested for 1,246 and 11,376 shares of common stock, respectively, with an aggregate acquisition-date fair value of $0.8 million and $7.1 million, respectively.

For the three and nine months ended September 30, 2017, the Company recorded stock-based compensation expense related to employee stock options of $0.2 million and $0.7 million, respectively, and $1.0 million and $6.3 million for the three and nine months ended September 30, 2016, respectively. As of September 30, 2017, there was $0.2 million of total future compensation costs related to unvested employee stock options to be recognized over a weighted-average period of 0.4 years.