Our 2014 Equity Incentive Plan (the “Plan”), provides for grants of equity incentive awards to our executive officers, non-employee directors, eligible employees and other key persons in order to attract, motivate and retain the talent for which we compete. Under the Plan, awards may be granted up to a maximum of 17,142,857 shares, if all awards granted are “full value awards,” as defined, and up to 34,285,714 shares, if all of the awards granted are “not full value awards,” as defined. “Full value awards” are awards such as restricted stock or long-term incentive plan LTIP units of our Operating Partnership (“LTIP units”) that do not require the payment of an exercise price. “Not full value awards” are awards such as stock options or stock appreciation rights that require the payment of an exercise price. As of December 31, 2019, we have 8,358,300 shares available for future grants under the Plan, if all awards granted are full value awards, as defined in the Plan.

The following table summarizes the components of stock-based compensation expense for the years ended December 31, 2019, 2018 and 2017.


	For the Year Ended December 31,
(Amounts in thousands)	2019		2018		2017
LTIP units	$	11,860	$	9,059	$	6,572
Performance-based units		8,477		7,645		6,421
Restricted stock		1,228		988		715
Stock options		1,295		1,954		2,214
Total stock-based compensation expense	$	22,860	$	19,646	$	15,922

We grant our executive officers, non-employee directors and other employees LTIP units which vest over a period of three to five years and are subject to a taxable book-up event, as defined. The LTIP units granted in the years ended December 31, 2019, 2018 and 2017 had grant date fair values of $13,091,000, $10,145,000 and $7,467,000, respectively, which are being amortized into expense on a straight-line basis over the vesting period. As of December 31, 2019, there was $12,854,000 of total unrecognized compensation cost related to unvested LTIP units, which is expected to be recognized over a weighted-average period of 2.6 years. The following table summarizes our LTIP unit activity for the year ended December 31, 2019.

	Units			Weighted-Average Grant-Date Fair Value
Unvested as of December 31, 2018		1,284,083		$	14.41
Granted		1,067,854			12.26
Vested		(752,645	)		13.73
Cancelled or expired		(27,828	)		13.13
Unvested as of December 31, 2019		1,571,464		$	13.30

We grant our executive officers and other employees LTIP units under multi-year performance-based long-term equity compensation programs. The purpose of these Performance Programs is to further align the interests of our stockholders with that of management by encouraging our senior officers to create stockholder value in a “pay for performance” structure. Under the Performance Programs, participants may earn LTIP units based on our Total Shareholder Return (“TSR”) over a three-year performance measurement period on both an absolute basis and relative basis. If the designated performance objectives are achieved, awards earned under the Performance Programs are subject to vesting over a period of four years and are also subject to a taxable book-up event, as defined.

The LTIPs unit activity granted under the Performance Programs in the years ended December 31, 2019, 2018 and 2017 had grant date fair values of $8,106,000, $7,009,000 and $10,520,000, respectively, and are being amortized into expense over the four-year vesting period using a graded vesting attribution method. As of December 31, 2019, there was $9,504,000 of total unrecognized compensation cost related to unvested LTIP units granted under the Performance Programs, which is expected to be recognized over a weighted average period of 2.4 years. The following table summarizes our LTIP unit activity granted under the Performance Programs for the year ended December 31, 2019.

	Units			Weighted-Average Grant-Date Fair Value (per unit)
Unvested as of December 31, 2018		3,373,570		$	7.27
Granted		1,356,630			5.98
Cancelled or expired		(1,134,366	)		8.05
Unvested as of December 31, 2019		3,595,834		$	6.54

On March 18, 2019, the Compensation Committee determined that the performance goals set forth in the 2015 Performance Program were not satisfied during the performance measurement period, which ended on March 17, 2019. Accordingly, all of the 1,109,358 LTIP units that were granted on March 18, 2016, were forfeited, with no awards being earned. This award had a grant date fair value of $10,914,000 and a remaining unrecognized compensation cost of $187,000 as of December 31, 2019, which will be recognized in the first quarter of 2020.

On January 17, 2020, the Compensation Committee determined that during the performance measurement period which ended on December 31, 2019, for the 2016 Performance Program, (i) the performance goals were not met on an absolute TSR basis and (ii) the performance goals met the 30^th percentile of the performance of the SNL Office REIT Index constituents on a relative basis. Accordingly, of the 1,085,244 LTIP units that were granted on January 30, 2017, 216,005 LTIP units were earned. Of the LTIP units earned, 107,996 LTIP units vested on January 17, 2020 and the remaining 108,009 LTIP units are subject to vesting based on continuous employment with us through December 31, 2020. This award had a grant date fair value of $10,520,000 and a remaining unrecognized compensation cost of $1,135,000 as of December 31, 2019, which will be amortized over a weighted-average period of 1.0 year.

On January 14, 2019, the Compensation Committee of our Board of Directors (the “Compensation Committee”) approved the 2018 Performance Program. Under the 2018 Performance Program, participants may earn awards in the form of LTIP units based on our TSR over a three-year performance measurement period beginning on January 1, 2019 and continuing through December 31, 2021, on both an absolute basis and relative basis. Awards granted to our Chief Executive Officer, under the 2018 Performance Program include an additional performance feature requiring threshold TSR performance on both an absolute and a relative basis in order for any awards to be earned. If the designated performance objectives are achieved, awards earned under the 2018 Performance Program are subject to vesting based on continued employment with us through December 31, 2022, with 50.0% of each award vesting upon the conclusion of the performance measurement period, and the remaining 50.0% vesting on December 31, 2022. Furthermore, our Named Executive Officers are required to hold earned awards for an additional year following vesting. The fair value of the awards granted under the 2018 Performance Program on the date of the grant was $8,106,000 and is being amortized into expense over the four-year vesting period using a graded vesting attribution method.

We grant shares of restricted stock to a non-employee director and certain other employees which vest over four years. The shares of restricted stock granted in the years ended December 31, 2019, 2018 and 2017 had grant date fair values of $1,238,000, $1,335,000 and $1,309,000, respectively, which are being amortized into expense on a straight-line basis over the vesting period. As of December 31, 2019, there was $1,823,000 of total unrecognized compensation cost related to restricted stock, which is expected to be recognized over a weighted-average period of 2.3 years. The table below summarizes our restricted stock activity for the year ended December 31, 2019.

	Shares			Weighted-Average Grant-Date Fair Value
Unvested as of December 31, 2018		162,981		$	15.26
Granted		93,308			13.27
Vested		(63,821	)		15.27
Cancelled or expired		(23,998	)		14.44
Unvested as of December 31, 2019		168,470		$	14.27

We did not grant any stock options in the years ended December 31, 2019 and 2018. Stock options granted in prior years to certain of our executive officers and other employees vest over periods ranging from three to five years and expire 10 years from the date of grant. The stock options granted in the year ended December 31, 2017 had grant date fair values of $4.02, which are being amortized into expense on a straight-line basis over the vesting period. The fair value of the option was estimated using an option-pricing model with the following weighted-average assumptions for grants in year ended December 31, 2017.


	For the Year Ended December 31,
		2017
Expected volatility		29.0%
Expected life		5.9 years
Risk free interest rate		2.2%
Expected dividend yield		2.3%

As of December 31, 2019, there was $60,000 of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized in the first quarter of 2020. The following table summarizes our stock option activity for year ended December 31, 2019.

	Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2018		2,131,943		$	17.08
Granted		-			-
Exercised		-			-
Cancelled or expired		(47,000	)		17.50
Outstanding as of December 31, 2019		2,084,943		$	17.07		5.7	$	-
Options vested and expected to vest as of December 31, 2019		2,073,791		$	17.07		5.7	$	-
Options exercisable as of December 31, 2019		1,939,398		$	17.07		5.6	$	-