17. STOCK-BASED COMPENSATION

Under our 2015 Stock Incentive Plan (the "2015 Plan"), 6,000,000 shares of Class A common stock are authorized for grants of stock options, restricted stock units ("RSU"), restricted stock and stock appreciation rights to employees and non-employee directors. In addition, any shares available under our Amended and Restated Stock Incentive Plan (which expired on June 1, 2015), including in respect of any awards that expire, terminate or are forfeited, will be available for awards under the 2015 Plan. Under the 2015 Plan, awards are made to employees and directors at the discretion of the Compensation Committee. Any awards previously issued under the Amended and Restated Stock Incentive Plan will continue to be governed by the terms of that plan.

The charge for stock-based compensation in our consolidated statements of operations and comprehensive income / loss was as follows:



	For The Year Ended December 31,
	2017		2016		2015
Stock-based compensation expense from continuing operations	$	4,280	$	3,383	$	2,311
Stock-based compensation expense from discontinued operations ⁽¹⁾	132		127		128


⁽¹⁾	All stock-based compensation expense from discontinued operations relate to employees of Croatia and Slovenia.

Stock Options

Grants of options allow the holders to purchase shares of Class A common stock at an exercise price, which is generally the market price prevailing at the date of the grant, with vesting between one and four years after the awards are granted. A summary of option activity for the year ended December 31, 2017 is presented below:



	Shares	Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
Outstanding at December 31, 2016	2,011,392	$	2.32	8.58	$	453
Outstanding at December 31, 2017	2,011,392	$	2.32	7.58	$	4,677
Vested or expected to vest at December 31, 2017	2,011,392	$	2.32	7.58	$	4,677
Exercisable at December 31, 2017	902,848	$	2.31	7.51	$	2,113

When options are vested, holders may exercise them at any time up to the maximum contractual life of the instrument which is specified in the option agreement. At December 31, 2017, the maximum life of options that were issued under the 2015 Plan was ten years. Upon providing the appropriate written notification, holders pay the exercise price and receive shares. Shares delivered in respect of stock option exercises are newly issued shares.

The fair value of stock options is estimated on the grant date using the Black-Scholes option-pricing model and recognized ratably over the requisite service period as a component of selling, general and administrative expenses. The aggregate intrinsic value (the difference between the stock price on the last day of trading of the fourth quarter of 2017 and the exercise prices multiplied by the number of in-the-money options) represents the total intrinsic value that would have been received by the option holders had they exercised all in-the-money options as at December 31, 2017. This amount changes based on the fair value of our Class A common stock.

There were no options granted during the year ended December 31, 2017.

As at December 31, 2017, there was US$ 1.2 million unrecognized compensation expense related to stock options which is expected to be recognized over a weighted-average period of 1.6 years.

The following table summarizes information about stock option activity during 2017, 2016, and 2015:



	2017			2016				2015
	Shares	Weighted Average Exercise Price (per share)		Shares		Weighted Average Exercise Price (per share)		Shares		Weighted Average Exercise Price (per share)
Outstanding at January 1	2,011,392	$	2.32	1,666,000		$	3.53	155,000		$	29.88
Awards granted	—	—		411,392		2.46		1,600,000		2.29
Awards forfeited	—	—		—		—		(20,000	)	23.12
Awards expired	—	—		(66,000	)	33.66		(69,000	)	28.23
Outstanding at December 31	2,011,392	$	2.32	2,011,392		$	2.32	1,666,000		$	3.53

Restricted Stock Units

Each RSU represents a right to receive one share of Class A common stock of the Company for each RSU that vests in accordance with a time-based vesting schedule, generally between one to four years from the date of grant. Upon vesting, shares of Class A common stock are issued from authorized but unissued shares. Holders of RSU awards are not entitled to receive cash dividend equivalents and are not entitled to vote. The grant date fair value of RSUs is calculated as the closing price of our Class A common shares on the date of grant and presented as a component of selling, general and administrative expenses.

The following table summarizes information about unvested RSUs as at December 31, 2017:



	Number of Shares / Units		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2016	2,542,625		$	2.61
Granted	1,158,887		3.62
Vested	(931,867	)	2.69
Forfeited	(75,582	)	1.53
Unvested at December 31, 2017	2,694,063		$	3.07

As at December 31, 2017 and December 31, 2016 there were 719,109 and 958,812, respectively, of unvested RSUs with performance conditions. No RSUs with performance conditions were granted or forfeited during the year ended December 31, 2017. As at December 31, 2017, the intrinsic value of unvested RSUs was US$ 12.5 million. Total unrecognized compensation cost related to unvested RSUs as at December 31, 2017 was US$ 4.6 million and is expected to be recognized over a weighted-average period of 1.8 years.