Share-Based Compensation (Tables)

The 2015 Performance-Based RSUs and 2014 Performance-Based RSUs (collectively, the “Performance-Based RSUs”) are scheduled to cliff vest at the end of a three-year service period subject to the compensation committee's determination that the Company has achieved the pre-defined FFO per share goals (the “performance conditions”) and upon the average annual relative total stockholder return versus a comparator group of Companies that consist of Companies in the SNL US REIT Office Index (the “market conditions”) for the three-year periods detailed in the table below. The number of Performance-Based RSUs ultimately earned, and therefore the compensation costs for these awards, can fluctuate from the original number of RSUs granted based upon the levels of achievement for both the FFO per share and relative total stockholder return metrics. During the 2015 and 2014 performance periods, the estimate of the number of RSUs earned were evaluated quarterly based on our forecasted level of achievement of the FFO per share hurdle. As of December 31, 2015, the FFO per share hurdle performance conditions were achieved at 1.5x target for both awards. As a result, the number of RSUs earned as of that date based on the FFO per share performance, excluding the impact of forfeitures, was as follows:



	2015 Performance-Based RSU Grant	2014 Performance-Based RSU Grant
Service vesting period	December 31, 2017	December 31, 2016
Target RSUs granted	127,657	119,098
Estimated RSUs earned based on FFO per share performance condition	185,510	178,650
Date of fair valuation	January 27, 2015	May 22, 2014

Each Performance-Based RSU represents the right to receive one share of our common stock in the future, subject to, and as modified by, the Company's level of achievement of the market condition. The fair value of the 2015 Performance-Based RSU Grant was $10.1 million at January 27, 2015 and the fair value of the 2014 Performance-Based RSU Grant was $7.7 million at May 22, 2014. The fair value for each grant was calculated using a Monte Carlo simulation pricing model based on the assumptions in the table below. The determination of the fair value of the Performance-Based RSU Grants take into consideration the likelihood of achievement of both the performance condition and the market condition discussed above. For the year ended December 31, 2015, we recorded compensation expense for the 2015 Performance-Based RSU Grant based upon the $78.55 fair value per share at January 27, 2015 multiplied by the 185,510 RSUs estimated to be earned at December 31, 2015 (which is net of forfeitures). For the years ended December 31, 2015 and 2014, we recorded compensation expense for the 2014 Performance-Based RSU Grant based upon the $65.03 fair value per share at May 22, 2014 multiplied by the 178,650 RSUs, excluding the impact of forfeitures, estimated to be earned at December 31, 2014. Compensation expense for the Performance-Based RSUs is recorded on a straight-line basis over the respective three-year periods. The following table summarizes the assumptions utilized in the Monte Carlo simulation pricing models:



	2015 Award Fair Value Assumptions	2014 Award Fair Value Assumptions
Valuation date	January 27, 2015	May 22, 2014
Fair value per share on valuation date	$78.55	$65.03
Expected share price volatility	20.00%	24.00%
Risk-free interest rate	0.92%	0.61%
Remaining expected life	2.9 years	2.6 years

The computation of expected volatility was based on a blend of the historical volatility of our shares of common stock over approximately five years, as this is expected to be most consistent with future volatility and equates to a time period twice as long as the approximate two and a half year remaining performance period of the RSUs and implied volatility data based on the observed pricing of six month publicly-traded options on shares of our common stock. The risk-free interest rate was based on the yield curve on zero-coupon U.S. Treasury STRIP securities in effect at January 27, 2015 and May 22, 2014.

A summary of our nonvested restricted stock activity from January 1, 2015 through December 31, 2015 is presented below:



	Nonvested Restricted Stock		Weighted-Average Grant Date Fair Value Per Share
Outstanding at January 1, 2015	85,061		$	47.05
Vested ⁽¹⁾	(24,264	)	46.39
Outstanding as of December 31, 2015	60,797		$	47.32

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(1)	The total shares vested includes 10,699 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the restricted shares that have vested. We accept the return of shares at the current quoted closing share price of the Company’s common stock to satisfy tax withholding obligations.

A summary of our nonvested and vested restricted stock activity for years ended December 31, 2015, 2014 and 2013 is presented below:



	Shares Granted			Shares Vested
Years ended December 31,	Nonvested Shares Issued	Weighted-Average Grant Date Fair Value Per Share		Vested Shares		Total Fair Value at Vest Date⁽¹⁾ (in thousands)
2015	—	$	—	(24,264	)	$	1,725
2014	213	51.35		(25,899	)	1,323
2013	—	—		(47,291	)	2,290

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(1)	Total fair value of shares vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the date of vesting.

On February 22, 2012, the Compensation Committee of the Company granted non-qualified stock options to certain key members of our senior management team, including our Executive Officers, to purchase an aggregate 1,550,000 shares of the Company’s common stock (the “February 2012” Grant) at an exercise price per share equal to $42.61, the closing price of the Company’s common stock on the grant date. The options will vest ratably in annual installments over a five year period, subject to continued employment through the applicable vesting date. The term of each option is ten years from the date of the grant. Dividends will not be paid on vested or unvested options. The options were granted pursuant to the 2006 Plan.

The fair value of each stock option granted is estimated on the date of grant using the Black-Scholes option pricing model based on the following assumptions for the February 2012 Grant.



	February 2012 Option Grant
Fair value of options granted per share	$9.20
Expected stock price volatility	33.00%
Risk-free interest rate	1.35%
Dividend yield	3.80%
Expected life of option	6.5 years

The computation of expected volatility is based on a blend of the historical volatility of our shares of common stock over a time period longer than the expected life of the option and implied volatility data based on the observed pricing of six-month publicly traded options on our shares of common stock. The risk-free interest rate is based on the yield curve on zero-coupon U.S. Treasury STRIP securities in effect at the grant date. The expected dividend yield is estimated by examining the average of the historical dividend yield levels over the expected life of the option and the current dividend yield as of the grant date. The expected life of the options is calculated as the average of the vesting term and the contractual term. During the year ended December 31, 2015, 298,000 stock options vested with a total fair value of $2.7 million. During the year ended December 31, 2014, 304,000 stock options vested with a total fair value of $2.8 million. During the year ended December 31, 2013, 308,000 stock options vested with a total fair value of $2.8 million.

A summary of our stock option activity related to the February 2012 grant from January 1, 2015 through December 31, 2015 is presented below:



	Number of Options		Exercise Price		Intrinsic Value (in millions) ⁽¹⁾
Outstanding at December 31, 2014	1,008,000		$	42.61	$	26.7
Exercised	(342,000	)	42.61		10.3
Forfeited	(56,000	)	42.61		1.3
Outstanding at December 31, 2015 ⁽²⁾	610,000		$	42.61	$	12.6

Options exercisable at December 31, 2015 ⁽³⁾	70,000		$	42.61	$	1.4

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(1)	The intrinsic value of a stock option is the amount by which the fair value of the underlying stock exceeds the exercise price of an option. The fair value of the underlying stock was determined by using the closing share price on the NYSE on the date of exercise, forfeiture or respective period end.


(2)	As of December 31, 2015, the average remaining life of stock options outstanding was 6.2 years


(3)	As of December 31, 2015, the average remaining life of stock options exercisable was approximately 6.2 years.

A summary of our market-measure based RSU activity for years ended December 31, 2015, 2014 and 2013 is presented below:



	RSUs Granted			RSUs Vested
Years ended December 31,	Non-Vested RSUs Granted	Weighted-Average Fair Value Per Share ⁽¹⁾		Vested RSUs		Total Vest-Date Fair Value (in thousands)
2015	191,483	$	79.25	—		$	—
2014	183,365	64.86		(16,338	)	1,092
2013	9,542	44.55		(16,338	)	811

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(1)	Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant. As discussed above, the 2014 Performance-Based RSU Grant was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014.

A summary of our market-measure based RSU activity from January 1, 2015 through December 31, 2015 is presented below:



	Nonvested RSUs				Vested RSUs	Total RSUs
	Amount		Weighted-Average Fair Value Per Share ⁽¹⁾		Vested RSUs	Total RSUs
Outstanding at January 1, 2015	247,089		$	58.77	—	247,089
Granted	191,483		79.25		—	191,483
Issuance of dividend equivalents ⁽²⁾	6,347		70.47		—	6,347
Forfeited	(19,467	)	69.20		—	(19,467	)
Outstanding as of December 31, 2015 ⁽³⁾	425,452		$	67.68	—	425,452

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(1)	Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant. As discussed above, the 2014 Performance-Based RSU Grant was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014.


(2)	Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement.

(3)

Outstanding RSUs as of December 31, 2015 represent the achievement of the maximum performance conditions and assumed target levels for the market conditions. The number of restricted stock units ultimately earned is subject to change based upon actual performance over the three-year vesting period. Dividend equivalents earned will vest along with the underlying award and are also subject to changes based on the number of RSUs ultimately earned for each underlying award.

A summary of our time-based RSU activity from January 1, 2015 through December 31, 2015 is presented below:



	Nonvested RSUs				Vested RSUs		Total RSUs
	Amount		Weighted Average Fair Value Per Share (1)		Vested RSUs		Total RSUs
Outstanding at January 1, 2015	340,997		$	51.04	907,355		1,248,352
Granted	98,802		74.49		—		98,802
Vested	(107,541	)	49.52		107,541		—
Settled ⁽²⁾					(78,887	)	(78,887	)
Issuance of dividend equivalents⁽³⁾	3,255		70.47		20,705		23,960
Forfeited	(17,064	)	53.50		—		(17,064	)
Canceled ⁽⁴⁾					(5,354	)	(5,354	)
Outstanding as of December 31, 2015	318,449		$	58.91	951,360		1,269,809

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(1)	Represents the grant-date fair value for all awards excluding the 2014 Time-Based RSU Grant. As discussed above, the 2014 Time-Based RSU Grant was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014.

(2)

Represents vested RSUs that were settled in shares of the Company’s common stock. Total shares settled include 20,042 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the RSUs settled. We accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy tax obligations.


(3)	Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement.


(4)	For shares vested but not yet settled, we accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy minimum statutory tax-withholding requirements related to either the settlement or vesting of RSUs in accordance with the terms of the 2006 Plan.

A summary of our time-based RSU activity for the years ended December 31, 2015, 2014 and 2013 is presented below:



	RSUs Granted			RSUs Vested
Year ended December 31,	Non-Vested RSUs Issued	Weighted-Average Grant Date Fair Value Per Share		Vested RSUs		Total Vest-Date Fair Value ⁽¹⁾ (in thousands)
2015	98,802	$	74.49	(107,541	)	$	7,528
2014	155,016	59.89		(116,447	)	6,675
2013	173,758	49.45		(89,873	)	4,495

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(1)	Total fair value of RSUs vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the day of vesting. Excludes the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement.