Trustmark has granted stock and incentive compensation awards and units subject to the provisions of the Stock and Incentive Compensation Plan (the Stock Plan). Current outstanding and future grants of stock and incentive compensation awards are subject to the provisions of the Stock Plan, which is designed to provide flexibility to Trustmark regarding its ability to motivate, attract and retain the services of key associates and directors. The Stock Plan also allows Trustmark to grant nonqualified stock options, incentive stock options, stock appreciation rights, restricted stock, restricted stock units and performance units to key associates and directors.

Trustmark’s performance awards vest over three years and are granted to Trustmark’s executive and senior management teams. Performance awards granted vest based on performance goals of return on average tangible equity and total shareholder return. Performance awards are valued utilizing a Monte Carlo simulation model to estimate fair value of the awards at the grant date. The Monte Carlo simulation was performed by an independent valuation consultant and requires the use of subjective modeling assumptions. These awards are recognized using the straight-line method over the requisite service period. These awards provide for achievement shares if performance measures exceed 100%. The restricted share agreement for these awards provides for voting rights and dividend privileges. During 2020, Trustmark began granting performance units instead of performance awards. The performance units have the same attributes as the previously granted performance awards, except for the performance units do not provide voting rights.

Trustmark’s time-vested awards vest over three years and are granted to members of Trustmark’s Board of Directors as well as Trustmark’s executive and senior management teams. Time-vested awards are valued utilizing the fair value of Trustmark’s stock at the grant date. These awards are recognized on the straight-line method over the requisite service period. During 2020, Trustmark began granting time-vested units instead of time-vested awards. The time-vested units have the same attributes as the previously granted time-vested awards, except for the time-vested units do not provide voting rights.

The following tables summarize the Stock Plan activity for the periods presented:

	Three Months Ended September 30, 2020
	Performance Awards and Units			Time-Vested Awards and Units
Nonvested shares, beginning of period		146,508			304,693
Granted		—			1,500
Released from restriction		—			(2,031	)
Forfeited		(1,640	)		(1,967	)
Nonvested shares, end of period		144,868			302,195

	Nine Months Ended September 30, 2020
	Performance Awards and Units			Time-Vested Awards and Units
Nonvested shares, beginning of period		149,914			300,006
Granted		53,450			123,060
Released from restriction		(36,357	)		(109,537	)
Forfeited		(22,139	)		(11,334	)
Nonvested shares, end of period		144,868			302,195

The following table presents information regarding compensation expense for awards and units under the Stock Plan for the periods presented ($ in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Performance awards and units	$	417	$	481	$	360	$	1,043
Time-vested awards and units		822		791		3,547		2,510
Total compensation expense	$	1,239	$	1,272	$	3,907	$	3,553