The Company awards equity-based compensation to employees and directors, which is recognized in the statements of operations based on the grant-date fair value of the award. The Company uses the straight-line method for recording compensation expense over a vesting period generally up to four years with either graded or cliff vesting. Stock compensation expense recognized during the period is based on the value of the portion of equity-based awards that is ultimately expected to vest during the period reduced by the unvested expense on awards forfeited during the period.

On May 4, 2018, the shareholders of the Company approved the adoption of the Gibraltar Industries, Inc. 2018 Equity Incentive Plan (the "2018 Plan"). The 2018 Plan provides for the issuance of up to 1,000,000 shares of common stock and supplements the remaining shares available for issuance under the existing Gibraltar Industries, Inc. 2015 Equity Incentive Plan (the "2015 Plan"). The Company's 2005 Equity Incentive Plan (the "Prior Plan") was amended in 2015 to terminate issuance of further awards from the Prior Plan.

Both the 2018 Plan and the 2015 Plan allow the Company to grant equity-based incentive compensation awards, in the form of non-qualified options, restricted shares, restricted stock units, performance shares, performance stock units, and stock rights to eligible participants.

In 2016, the shareholders of the Company approved the adoption of the Gibraltar Industries, Inc. 2016 Stock Plan for Non-Employee Directors ("Non-Employee Directors Plan") which allows the Company to grant awards of shares of the Company's common stock to non-employee Directors of the Company and permits the Directors to defer receipt of such shares pursuant to the terms of the Non-Employee Directors Plan.

At December 31, 2019, 699,000 and 157,000 shares were available for issuance under the 2018 Plan and 2015 Plan, respectively, as incentive stock options or other stock awards, and 45,000 shares were available for issuance under the Non-Employee Directors Plan as awards of shares of the Company's common stock.

The Company recognized the following compensation expense in connection with awards that vested under the 2018 Plan, the 2015 Plan, the Prior Plan, and the Non-Employee Directors Plan along with the related tax benefits recognized during the years ended December 31 (in thousands):



	2019		2018		2017
Expense recognized under the Prior Plan	$	192	$	569	$	1,059
Expense recognized under the 2015 Plan	5,077		7,988		5,643
Expense recognized under the 2018 Plan	6,731		188		—
Expense recognized under the Non-Employee Directors Plan	570		444		420
Total stock compensation expense	$	12,570	$	9,189	$	7,122
Tax benefits recognized related to stock compensation expense	$	3,136	$	2,509	$	2,133

The following table provides the number of stock options, stock units, and common stock granted during the years ended December 31, along with the weighted-average grant-date fair value of each award:



	2019			2018			2017
Awards	Number of Awards	Weighted Average Grant Date Fair Value		Number of Awards	Weighted Average Grant Date Fair Value		Number of Awards	Weighted Average Grant Date Fair Value
Options	—	$	—	—	$	—	25,000	$	12.85
Deferred stock units	7,509	$	37.95	10,255	$	35.96	10,170	$	34.42
Common stock	7,509	$	37.95	2,113	$	35.50	2,034	$	34.42
Restricted stock units	152,472	$	39.73	116,174	$	36.61	133,548	$	36.56
Performance stock units	183,908	$	40.49	135,929	$	33.63	108,748	$	42.72

The fair value of stock options granted during the year ended December 31, 2017 was estimated on the date of grant using the Black-Scholes option pricing model. No options were granted in 2019 and 2018. Expected stock volatility was based on volatility of the Company’s stock price using a historical period commensurate with the expected life of the options. The following table provides the weighted average assumptions used to value stock options issued during the year ended December 31:

The following table summarizes the ranges of outstanding and exercisable options at December 31, 2019:



Range of Exercise Prices	Options Outstanding	Weighted Average Remaining Contractual Life (in years)	Weighted Average Exercise Price		Options Exercisable	Weighted Average Exercise Price
$8.90 – $9.50	15,938	0.71	$	8.90	15,938	$	8.90
$9.51 – $24.00	51,471	1.71	$	9.74	51,471	$	9.74
$24.01 – $25.50	25,000	6.01	$	25.44	25,000	$	25.44
$25.51 - $43.05	25,000	7.13	$	42.35	—	$	—
	117,409				92,409

The following table summarizes information about stock option transactions:



	Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value
Balance at January 1, 2017	277,224		$	14.95
Granted	25,000		42.35
Exercised	(42,058	)	16.02
Forfeited	(12,500	)	25.44
Balance at December 31, 2017	247,666		$	17.01
Exercised	(87,907	)	15.75
Balance at December 31, 2018	159,759		$	17.70
Exercised	(42,350	)	11.57
Balance at December 31, 2019	117,409		$	19.91	3.64	$	3,584,000

The aggregate intrinsic value in the preceding table represents the total pre-tax intrinsic value, based on the $50.44 per share market price of the Company’s common stock as of December 31, 2019, which would have been received by the option holders had all option holders with an exercise price below the per share market price on December 31, 2019, exercised their options as of that date.



	Restricted Stock Units		Weighted Average Grant Date Fair Value		Common Stock		Weighted Average Grant Date Fair Value		Performance Stock Units (1)		Weighted Average Grant Date Fair Value		Deferred Stock Units (2)	Weighted Average Grant Date Fair Value
Balance at December 31, 2018	395,353		$	27.61	—		$	—	235,485		$	33.78	27,243	$	33.18
Granted	152,972		39.73		7,509		37.95		194,658		40.49		7,509	37.95
Vested	(162,690	)	24.31		(7,509	)	37.95		(92,696	)	28.99		—	—
Forfeited	(11,203	)	35.72		—		—		(8,190	)	46.05		—	—
Balance at December 31, 2019	374,432		$	33.74	—		$	—	329,257		$	38.53	34,752	$	34.21

(1) The Company’s performance stock units (“PSUs”) represent shares granted for which the final number of shares earned depends on financial performance or market conditions. The number of shares to be issued may vary between 0% and 200% of the number of performance stock units granted depending on the relative achievement to targeted thresholds. The Company's PSUs with a financial performance condition are based on either the Company’s return on invested capital (“ROIC”) over a one-year period performance period or revenue and gross profit thresholds over a two-year performance period. The Company's PSUs with a market condition are based on the ranking of the Company’s total shareholder return (“TSR”) performance, on a percentile basis, over a three year performance period compared to the S&P Small Cap Industrial sector, over the same three year performance period.

The fair value of the common stock, restricted stock units, and deferred stock units, as well as the performance stock units with a financial performance condition granted during the three years ended December 31, 2019 was based on the Company stock price at grant date of the award. The fair value of the performance stock units with a market condition granted during the three years ended December 31, 2019 were determined using a Monte Carlo simulation as of the grant date of the award, however, no such awards were granted in 2019 and 2018.

The following table sets forth the aggregate intrinsic value of options exercised and aggregate fair value of restricted stock units and restricted shares that vested during the years ended December 31 (in thousands):



	2019		2018		2017
Aggregate intrinsic value of options exercised	$	1,371	$	2,128	$	628
Aggregate fair value of vested restricted stock units	$	10,017	$	5,307	$	6,756
Aggregate fair value of vested common and restricted shares	$	285	$	149	$	70
Aggregate fair value of vested deferred stock units	$	285	$	369	$	350

As of December 31, 2019, there was $10.9 million of total unrecognized compensation cost related to non-vested options, restricted shares, and restricted stock units. That cost is expected to be recognized over a weighted average period of 2.2 years.

As of December 31, 2019, the Company's total share-based liabilities recorded on the consolidated balance sheet was $28.0 million, of which $14.8 million was included in current accrued expenses and $13.2 million was included in non-current liabilities. Total share-based liabilities as of December 31, 2018 were $38.4 million, of which $23.6 million was included in non-current liabilities. At December 31, 2019, the Company's equity based awards that are settled in cash are the awards under the management stock purchase plan.

During the year ended December 31, 2019, the Company paid $8.9 million to participants that were awarded cash-settled performance stock units in 2016. The participants earned 200% of target, or 256,000 units, which were converted to cash and valued at the trailing 90-day closing price of the Company's common stock as of December 31, 2018.

The Management Stock Purchase Plan ("MSPP") provides participants the ability to defer a portion of their compensation, convertible to unrestricted investments, restricted stock units, or a combination of both, or defer a portion of their Directors’ fees, convertible to restricted stock units. Employees eligible to defer a portion of their compensation also receive a company-matching award in restricted stock units equal to a percentage of their deferred compensation.

The deferrals and related company match are credited to an account that represents a share-based liability. The portion of the account deferred to unrestricted investments is measured at fair market value of the unrestricted investments, and the portion of the account deferred to restricted stock units and company-matching restricted stock units is measured at a 200-day average of the Company stock price. The account will be converted to and settled in cash payable to participants upon retirement or a termination of their service to the Company.

The following table provides the number of restricted stock units credited to active participant accounts, balance of vested and unvested restricted stock units within active participant accounts, payments made with respect to restricted stock units issued under the MSPP, and MSPP expense during years ended December 31:



	2019		2018		2017
Restricted stock units credited	61,369		66,843		84,299
Restricted stock units balance, vested and unvested	415,760		387,870		389,189
Share-based liabilities paid, in thousands	$	6,543	$	5,232	$	6,058
MSPP expense, in thousands	$	2,699	$	4,809	$	2,432