STOCK-BASED COMPENSATION

All stock-based awards are subject to the terms of the 2009 Performance Incentive Plan, which was assumed by the Company effective as of November 15, 2010 in connection with the Company's separation from Sun and amended and restated in June 2013. The 2009 Performance Incentive Plan provides for the granting of stock-based compensation, including stock options, time-based stock units, funds from operations-based stock units ("FFO Units"), relative total stockholder return-based stock units ("TSR Units") and performance based restricted stock units to officers, employees and directors in connection with their employment with or services provided to the Company.

Stock Options

The total intrinsic value of stock options exercised was $0.7 million during the year ended December 31, 2014. The exercise price for the stock options exercised during the year ended December 31, 2014 was paid through the withholding of shares. The total fair value of stock options that vested during the year ended December 31, 2014 was $0.2 million. The Company had no stock options outstanding during the years ended December 31, 2016 and 2015 .

Restricted Stock Units and Performance-Based Restricted Stock Units

Under the 2009 Performance Incentive Plan, restricted stock units and performance-based restricted stock units generally have a contractual life or vest over a three- to five-year period. The vesting of certain restricted stock units may accelerate, as defined in the grant, upon retirement, a change in control and other events. When vested (and subject to any applicable deferral or holdback period), each performance-based restricted stock unit is convertible into one share of common stock, subject to any deferrals in issuance pursuant to the grant. The restricted stock units are valued on the grant date based on the market price of the Company's common stock on that date. Generally, the Company recognizes the fair value of the awards over the applicable vesting period as compensation expense. In addition, since the shares to be issued may vary based on the performance of the Company, the Company must make assumptions regarding the projected performance criteria and the shares that will ultimately be issued. The amount of FFO Units that will ultimately vest is dependent on the amount by which the Company's funds from operation ("FFO") differs from a target FFO amount for a period specified in each grant and will range from 0% to 250% of the FFO Units initially granted. Similarly, the amount of TSR Units that will ultimately vest is dependent on the amount by which the total shareholder return ("TSR") of the Company's common stock differs from a predefined peer group for a period specified in each grant and will range from 0% to 200% of the TSR Units initially granted. Upon any payment of restricted stock units, the participant is required to pay the related tax withholding obligation. The 2009 Performance Incentive Plan provides that unless otherwise elected in advance by the participant, the Company will reduce the number of shares to be delivered to pay the related statutory tax withholding obligation. The value of the shares withheld is dependent on the closing price of the Company's common stock on the date the relevant transaction occurs.

The following table summarizes additional information concerning restricted stock units at December 31, 2016:



	Restricted Stock Units		Weighted Average Grant Date Fair Value Per Unit
Unvested as of December 31, 2015	732,756		$	21.37
Granted	393,532		22.05
Vested	(214,671	)	22.01
Dividends reinvested	73,888		22.07
Cancelled/Forfeited	(81,538	)	21.13

Unvested as of December 31, 2016	903,967		$	21.58

As of December 31, 2016, the weighted average remaining vesting period of restricted stock units was 2.2 years. The weighted average fair value per share at the date of grant for restricted stock units for the years ended December 31, 2016, 2015 and 2014 was $22.05, $21.11 and $25.88, respectively. The total fair value of units vested during the years ended December 31, 2016, 2015 and 2014 was $4.7 million, $8.5 million and $9.6 million, respectively.

The fair value of the TSR Units are estimated on the date of grant using a Monte Carlo valuation model that uses the assumptions noted in the table below. The risk-free rate is based on the U.S. Treasury yield curve in effect at the grant date for the expected performance period. Expected volatility was based on historical volatility for the most recent 3-year period ending on the grant date for the Company and the selected peer companies, and calculated on a daily basis. The following are the key assumptions used in this valuation:



	2016		2015		2014
Risk Free Interest Rate	0.78% - 1.60%		0.87% - 1.31%		1.07% - 1.09%
Expected Stock Price Volatility	27.40% - 28.42%		23.55% - 27.02%		24.14% - 24.22%
Expected Service Period	2.3 - 3.0 years		2.5 - 3.0 years		3.0 years
Expected Dividend Yield (assuming full reinvestment)	—	%	—	%	—	%

During the years ended December 31, 2016, 2015 and 2014, the Company recognized $7.5 million, $6.1 million and $9.9 million, respectively, of stock-based compensation expense. As of December 31, 2016, there was $10.4 million of total unrecognized stock-based compensation expense related to unvested awards, which is expected to be recognized over a weighted average period of 2.6 years.

Employee Benefit Plan

The Company maintains a 401(k) plan that allows for eligible participants to defer compensation, subject to certain limitations imposed by the Internal Revenue Code of 1986, as amended (the “Code”). The Company provides a discretionary matching contribution of up to 3% of each participant's eligible compensation. During the years ended December 31, 2016, 2015 and 2014, the Company's matching contributions were approximately $73,000, $35,000 and $51,000, respectively.