On April 9, 2019, the Company’s board of directors authorized a stock repurchase program to acquire up to $15.0 million of its common stock. Any repurchases under the program will be made from time to time on the open market at prevailing market prices. During the year ended December 31, 2019, the Company repurchased 0.3 million shares of its common stock for a total cost of $2.5 million.

On October 30, 2013, the Board of Directors adopted, and on December 27, 2013, the stockholders approved, the 2013 Stock-Based Incentive Compensation Plan (the “2013 Plan”), that became effective upon consummation of the Merger on January 15, 2014 and was subsequently amended at our 2019 Annual Meeting. Our stock-based compensation program is a broad-based program designed to attract and retain employees while also aligning employees’ interests with the interests of our shareholders. In addition, members of our Board of Directors participate in our stock-based compensation program in connection with their service on our board.

Stock option awards outstanding under the 2013 Plan are time-based and granted at exercise prices which are equal to the market value of the Company’s common stock on the grant date and expire no later than ten years from the date of grant, but only to the extent they have vested. The options generally vest as specified in the option agreements subject, in some instances, to acceleration in certain circumstances. The restrictions on restricted stock generally lapse over a three-year period from the date of the grant. In the event a participant terminates employment with the Company, any vested stock options and any restricted stock still subject to restrictions are generally forfeited if they are not exercised within 90 days.

The following table presents the stock activity and the total number of shares available for grant as of December 31, 2019:

	(in thousands)
Balance at December 31, 2018		1,201
Plan amendment		1,440
Options granted		(627	)
Restricted stock granted		(292	)
Forfeited/Expired shares added back		55
Balance at December 31, 2019		1,777

Total estimated stock-based compensation expense for employees and non-employees, related to all of the Company's stock-based awards, was comprised as follows:

	Year ended December 31,
	2019		2018		2017
	(in thousands)
Cost of revenue	$	150	$	289	$	(66	)
Selling and marketing		691		186		100
Research and development		417		136		232
General and administrative		2,300		1,266		1,164
Total stock-based compensation	$	3,558	$	1,877	$	1,430

Forfeitures on option grants are estimated at 10% based on evaluation of historical and expected future turnover for non-executives and 0% for executives. Stock-based compensation expense was recorded net of estimated forfeitures, such that expense was recorded only for those stock-based awards that are expected to vest. The Company reviews this assumption periodically and will adjust it if it is not representative of future forfeiture data and trends within employee types (executive vs. non-executive).

In 2017, due to changes in the reporting of stock compensation, the Company’s previously unrecognized excess tax benefit related to the exercise of nonqualified stock options totaling $2.2 million was recognized as a deferred tax asset. The associated tax benefit recognized in the Consolidated Statements of Operations for the fiscal years ended December 31, 2019 and 2018 was approximately $0.1 million and $1.2 million, respectively.

	Options Outstanding
	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2018		1,654,729		$	6.41		7.36	$	14,374,572
Granted		626,636			11.45
Exercised		(88,927	)		3.71
Forfeited		(49,513	)		13.57
Outstanding at December 31, 2019		2,142,925		$	7.83		7.13	$	6,545,982
Vested and expected to vest at December 31, 2019		2,091,287		$	7.82		7.09	$	6,451,094
Exercisable at December 31, 2019		1,063,745		$	6.54		5.48	$	3,926,696

Aggregate intrinsic value represents the difference between the estimated fair value of the underlying common stock and the exercise price of outstanding, in-the-money options. The aggregate intrinsic value of options exercises was $0.6 million and $9.0 million for the years ended December 31, 2019 and 2018, respectively.

As of December 31, 2019, total unrecognized compensation cost related to non-vested stock options granted to employees was $3.5 million, which is expected to be recognized over a remaining weighted average vesting period of 2.7 years.

Option valuation models require the input of highly subjective assumptions, including expected stock price volatility. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options, which have no vesting restrictions and are fully transferable. The fair value of options granted under the 2013 Plan was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions:

Each of these inputs is subjective and generally requires significant judgment to determine. The risk-free rate is based on a zero-coupon U.S. Treasury rate in effect at the time of grant with maturity dates that coincide with the expected life of the options. The expected life of the options is based on a simplified weighted average taking into account the vesting conditions and contractual life of the award. Since the Company has a limited trading history for its common stock, the expected volatility was derived from the historical stock volatilities of several unrelated public companies within the Company’s industry that are considered to be comparable to the Company’s business over a period equivalent to the expected term of the stock option grants.

The weighted average grant date fair value of options granted during the three years ended December 31, 2019 was $4.71, $3.33, and $0.29, respectively. The total estimated fair value of employee options vested during the three years ended December 31, 2019 was $1.0 million, $0.7 million and $1.3 million, respectively.

	Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested restricted stock at December 31, 2018		265,636		$	19.29
Granted		292,423			11.51
Vested		(131,594	)		15.80
Shares forfeited		(4,975	)		12.10
Nonvested restricted stock at December 31, 2019		421,490		$	15.06

As of December 31, 2019 total unrecognized compensation cost related to the nonvested restricted stock awards granted was $5.5 million, which is expected to be recognized over a remaining weighted average vesting period of 2.6 years.

In connection with certain subordinated notes, the Company issued warrants to purchase an aggregate 0.4 million shares and 0.3 million shares of the Company’s common stock at an exercise price of $10.16 and $8.00 per share, respectively, to SG VTB Holdings, LLC, all of which were settled through cashless exercises during the year ended December 31, 2019.

In connection with the retirement of the Series B Preferred Stock in April 2018, the Company issued wholly-funded warrants exercisable for an aggregate of 0.5 million shares of its common stock. Under the terms of the warrants, the holders had the right to receive, at their option, a cash payment for the remaining unexercised portion of the warrants upon the Company consummating a Fundamental Transaction (as defined in the warrant agreement, and including any merger, consolidation, sale or other reorganization event in which its common stock is converted into or exchanged for securities, cash or other property). If so elected by the warrant holders, the cash payment will be based on a Black-Scholes pricing model and will be made upon the consummation of a Fundamental Transaction or during the ensuing 30-day period thereafter. As a result of these terms regarding the possible future cash payment, the Company accounted for the warrants issued in connection with the retirement of the Series B Preferred Stock as a financial instrument obligation that is marked to market each period, with subsequent changes in fair value reported in earnings.

On March 30, 2019, the Company and the warrant holders entered into an amendment to the warrant agreement that revises the terms under which warrant holders may exercise their rights under a Fundamental Transaction. As a result of this amendment, the warrants are no longer accounted for as a financial instrument obligation and reported as a liability that is marked to market each period with changes in fair value reported in earnings. The warrants were marked to market through March 30, 2019, the execution date of the amendment, at which time the warrants are accounted for as an equity instrument. The fair value on that date of $6.2 million was reclassified to additional paid-in-capital. For the years ended December 31, 2019 and 2018, the Company recognized an unrealized gain of $1.6 million and unrealized loss of $5.3 million, respectively, on the warrants that is included in “Other non-operating expense (income), net” in the Condensed Consolidated Statement of Operations.

In November 2011, VTBH adopted a 2011 Phantom Equity Appreciation Plan (“the Appreciation Plan”) that covers certain employees, consultants, and directors of VTBH (“Participants”) who are entitled to phantom units, as applicable, pursuant to the provisions of their respective award agreements. The Appreciation Plan is shareholder-approved, which permits the granting of phantom units to Participants of up to 1,500,000 units. These units are not exercisable or convertible into shares of common stock, but give the holder a right to receive a cash bonus equal to the appreciation in value between the exercise price and value of common stock at the time of a change in control event as defined in the plan.

As of December 31, 2019 and 2018, 178,586 phantom units at a weighted-average exercise price of $3.72 have been granted and are outstanding. Because these phantom units are not exercisable or convertible into common shares, the share amounts and exercise prices were not subject to the exchange ratio provided by the Merger agreement. As of December 31, 2019, compensation expense related to the Appreciation Plan units remained unrecognized because a change in control of VTB, as defined in the plan, had not occurred and is not anticipated by the Company. In July 2015, the Appreciation Plan was terminated as to new grants, but vested phantom units remain in place.