NOTE 15. STOCK-BASED COMPENSATION

The Company’s 2017 Stock Incentive Plan, or the 2017 Plan, permits stock-based compensation awards to officers, directors, key employees, and consultants. The 2017 Plan authorized grants of stock‑based compensation instruments to issue up to 4,000,000 shares of Company common stock. As of December 31, 2017, there were 3,638,497 shares available for grant under the 2017 Plan. Though frozen for new issuances, certain awards issued under the 2003 Stock Incentive Plan, or the 2003 Plan, remain outstanding.

Restricted Stock

Restricted stock amortization totaled $24.9 million, $22.7 million and $15.0 million for the years ended December 31, 2017, 2016 and 2015. Such amounts are included in compensation expense on the accompanying consolidated statements of earnings. The income tax benefit recognized in the consolidated statements of earnings related to this expense was $8.9 million, $8.4 million, and $5.6 million for the years ended December 31, 2017, 2016 and 2015. The amount of unrecognized compensation expense related to all unvested TRSAs and PRSUs as of December 31, 2017 totaled $49.0 million. Such expense is expected to be recognized over a weighted average period of 1.5 years.

The following table presents a summary of restricted stock transactions during the year ended December 31, 2017:



	TRSAs			PRSUs
			Weighted		Weighted
			Average		Average
			Grant Date		Grant Date
	Number of		Fair Value	Number of	Fair Value
	Shares		(Per Share)	Units	(Per Unit)
Unvested restricted stock, December 31, 2016	1,476,132		$39.83	153,715	$27.32
Granted	557,955		$50.08	85,310	$57.80
Vested	(498,186	)	$40.20	—	$—
Forfeited	(99,781	)	$42.87	—	$—
Unvested restricted stock, December 31, 2017	1,436,120		$43.47	239,025	$38.20

Time-Based Restricted Stock Awards

At December 31, 2017, there were 1,436,120 shares of unvested TRSAs outstanding pursuant to the Company's 2003 and 2017 Stock Incentive Plans (the "Plans"). The TRSAs generally vest over a service period of three to four years from the date of the grant or immediately upon death of an employee. For awards granted before December 11, 2014, time-based restricted common stock also vests immediately upon a change in control of the Company, as defined in the Plans. Grants issued on or after December 11, 2014, are subject to "double-trigger" vesting, meaning that, in the event of a change in control of the Company, as defined in the Plans, and in the event an employee's employment is terminated within 24 months after the change in control by the Company without Cause or by the employee for Good Reason, as defined in the Plans, such awards will vest. Compensation expense related to TRSAs is based on the fair value of the underlying stock on the award date and is recognized over the vesting period using the straight‑line method.

The weighted average grant date fair value per share of TRSAs granted during 2017, 2016 and 2015 were $50.08, $36.05 and $46.18. The vesting date fair value of TRSAs that vested during 2017, 2016 and 2015 were $24.9 million, $14.4 million and $14.7 million.

Performance-Based Restricted Stock Units

At December 31, 2017, there were 239,025 units of unvested PRSUs that have been granted. The PRSUs will vest only if performance goals with respect to certain financial metrics are met over a three-year performance period. The PRSUs are not considered issued and outstanding under the 2003 Stock Incentive Plan until they vest. PRSUs are granted and initially expensed based on a target number. The number of shares that will ultimately vest based on actual performance will range from zero to a maximum of either 150% or 200% of target. Compensation expense related to PRSUs is based on the fair value of the underlying stock on the award date and is amortized over the vesting period using the straight-line method unless it is determined that: (1) attainment of the financial metrics is less than probable, in which case a portion of the amortization is suspended, or (2) attainment of the financial metrics is improbable, in which case a portion of the previously recognized amortization is reversed and also suspended. If it is determined that attainment of a financial measure higher than target is probable, the amortization will increase up to 150% or 200% of the target amortization amount. Annual PRSU expense may vary during the three-year performance period based upon changes in management's estimate of the number of shares that may ultimately vest. In the case where the performance target for the PRSU’s is based on a market condition (such as total shareholder return), the amortization is neither reversed nor suspended if it is subsequently determined that the attainment of the performance target is less than probable or improbable.

Upon a change in control, each PRSU will (i) be deemed earned at the target level with respect to all open performance periods if the change in control occurs within six months after the grant date, and (ii) be deemed earned at the actual performance level as of the date of the change in control if a change in control occurs more than six months after the grant date, and in both cases, the PRSU will cease to be subject to any further performance conditions, but will be subject to time-based service vesting following the change in control in accordance with the original performance period.

The weighted average grant date fair value per share of PRSUs granted during 2017 and 2016 was $57.80 and $27.32. There were no grants of PRSUs prior to 2016. There were no PRSUs that vested during 2017, 2016, and 2015.