Share-Based Compensation

On May 22, 2007, our stockholders adopted a Long-Term Incentive Plan (“LTIP”) which provided an additional 3.3 million shares that could be granted in the form of stock options, stock appreciation rights, restricted stock awards, performance units and performance awards, in addition to the shares from the previous plan, the 1992 Plan. Since inception of the LTIP, non-qualified stock options and restricted stock awards have been granted with a five year vesting schedule. Under the LTIP, the exercise price of shares granted may not be less than 100% of the fair market value at the date of the grant.

On May 24, 2016, our stockholders adopted the 2016 Long-Term Incentive Plan (“2016 Plan”) which provides for approximately 6.4 million shares, comprised of 3.4 million new shares provided for under the 2016 Plan, approximately 0.4 million shares that were available for issuance under the previous LTIP that are now authorized for issuance under the 2016 Plan, and an additional 2.6 million shares that were approved by the stockholders on May 15, 2018. Under the 2016 Plan, shares can be granted in the form of stock options, stock appreciation rights, restricted stock awards, performance awards, dividend equivalent rights, and other awards. Under the 2016 Plan, the exercise price of shares granted may not be less than 100% of the fair market value at the date of the grant. The 2016 Plan is administered by the Compensation Committee of the Board of Directors or such other committee of the Board of Directors as is designated by the Board of Directors (the “Committee”). Membership on the Committee is limited to independent directors. The Committee may delegate certain duties to one or more officers of the Company as provided in the 2016 Plan. The Committee determines the persons to whom awards are to be made, determines the type, size and terms of awards, interprets the 2016 Plan, establishes and revises rules and regulations relating to the 2016 Plan and makes any other determinations that it believes necessary for the administration of the 2016 Plan.

The total pre-tax compensation cost related to unvested stock options not yet recognized as of December 31, 2018 is $14.3 million and is expected to be recognized over a weighted-average period of 2.29 years.

The following weighted average assumptions were used to determine the fair value of the stock options granted on the original grant date for expense recognition purposes for options granted during December 31, 2018, 2017, and 2016 using a Black Scholes-Merton Model:



	2018			2017			2016

Director and Officers:
Expected dividend yield	$	0.26		$	0.26		$	0.22
Expected volatility	29.73		%	30.81		%	41.19		%
Risk-free interest rate	2.20		%	1.90		%	2.00		%
Expected life (in years)	5.00			5.00			7.68
Employees:
Expected dividend yield	$	0.26		$	0.26		$	0.25
Expected volatility	29.82		%	30.67		%	34.50		%
Risk-free interest rate	2.51		%	1.89		%	1.73		%
Expected life (in years)	5.00			5.00			5.69

The expected term of the options is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rate is based on the U.S. Treasury rates at the date of grant with maturity dates approximately equal to the expected life at the grant date. Volatility is based on historical volatility of our stock over time periods equal to the expected life at grant date.

The following is a summary of stock options vested and exercisable as of December 31, 2018:



		Weighted Average	Weighted
Range of	Number	Remaining	Average
Exercise	of	Contractual	Exercise		Intrinsic
Prices	Shares	Life	Price		Value
					(in thousands)
$5.67 - 32.80	456,223	5.72	$	20.25	$	6,757
$32.85 - 34.10	42,552	7.47	33.95		47
$34.15 - 42.94	17,202	8.30	35.19		7
Total	515,977	5.95	$	21.88	$	6,811

The following is a summary of stock options vested and exercisable as of December 31, 2017:



		Weighted Average	Weighted
Range of	Number	Remaining	Average
Exercise	of	Contractual	Exercise		Intrinsic
Prices	Shares	Life	Price		Value
					(in thousands)
$4.54 - 22.76	424,130	4.36	$	12.41	$	10,303
$23.57 - 32.85	107,456	8.31	30.10		709
$32.90 - 37.30	25,725	9.19	34.07		68
Total	557,311	5.35	$	16.82	$	11,080

The following is a summary of stock options vested and exercisable as of December 31, 2016:



		Weighted Average	Weighted
Range of	Number	Remaining	Average
Exercise	of	Contractual	Exercise		Intrinsic
Prices	Shares	Life	Price		Value
					(in thousands)
$4.54 - 20.92	338,308	4.75	$	8.03	$	8,465
$20.96 - 26.50	71,928	8.56	22.50		759
Total	410,236	5.42	$	10.57	$	9,224

A summary of option activity under the plans is as follows:



			Weighted Average Exercise
Options	Shares		Price

Outstanding at December 31, 2017	1,567,109		$	25.27
Granted	1,480,490		34.49
Exercised	(282,598	)	17.64
Forfeited or Expired	(319,152	)	32.84
Outstanding at December 31, 2018	2,445,849		$	30.77
Exercisable at December 31, 2018	515,977		$	21.89

The total intrinsic value of options exercised during the year ended December 31, 2018, 2017, and 2016 was $5.4 million, $4.5 million, and $4.9 million, respectively. The cash received from options exercised during the year eneded December 31, 2018, 2017, and 2016 was $5.0 million, $2.3 million, and $2.1 million, respectively. The impact of these cash receipts is included in financing activities in the accompanying Consolidated Statements of Cash Flows.

Since 2007, as part of the LTIP and since May 2016 as part of the 2016 Plan, the Compensation Committee of the Board of Directors has authorized and issued restricted stock awards to directors and certain key employees. Restricted stock awards granted to directors vest one-third each year. All other restricted stock awards vest at a rate of 20% per year. The fair value of restricted stock awards is based on the fair market value of AAON common stock on the respective grant dates, reduced for the present value of dividends.

These awards are recorded at their fair value on the date of grant and compensation cost is recorded using straight-line vesting over the service period. At December 31, 2018, unrecognized compensation cost related to unvested restricted stock awards was approximately $6.1 million which is expected to be recognized over a weighted average period of 1.84 years.

A summary of the unvested restricted stock awards is as follows:



			Weighted Average Grant date
Restricted stock	Shares		Fair Value

Unvested at December 31, 2017	341,800		$	25.52
Granted	112,075		32.20
Vested	(124,508	)	23.61
Forfeited	(36,917	)	28.37
Unvested at December 31, 2018	292,450		$	28.54

A summary of share-based compensation is as follows for the years ending December 31, 2018, 2017, and 2016:



	2018		2017		2016
Grant date fair value of awards during the period:	(in thousands)
Options	$	12,932	$	3,699	$	6,102
Restricted stock	3,609		4,217		3,147
Total	$	16,541	$	7,916	$	9,249



	2018		2017		2016
Share-based compensation expense:	(in thousands)
Options	$	4,181	$	2,904	$	1,681
Restricted stock	3,193		3,554		2,676
Total	$	7,374	$	6,458	$	4,357



	2018		2017		2016
Income tax benefit related to share-based compensation:	(in thousands)
Options	$	980	$	1,413	$	1,610
Restricted stock	353		1,051		458
Total	$	1,333	$	2,464	$	2,068