STOCKHOLDERS’ EQUITY (DEFICIT)

Stock Options

The fair value for options granted at the time of issuance were estimated at the date of grant using a Black-Scholes options pricing model. Significant assumptions included in the option value model include the fair value of our common stock at the grant date, weighted average volatility, risk-free interest rate, dividend yield and the forfeiture rate. There were no stock options granted in any of the periods presented.

Our stock option activity and related information are summarized as follows:



	Options		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Terms (in Years)
Outstanding at January 1, 2015	253,164		$	23.90	4.4
Forfeited or expired	(4,293	)	$	28.14
Outstanding at December 31, 2015	248,871		$	23.82	3.4
Forfeited or expired	(670	)	$	30.97
Outstanding at December 31, 2016	248,201		$	23.81	2.4
Forfeited or expired	(71,242	)	$	9.85
Outstanding at December 31, 2017	176,959		$	29.42	2.0

Options generally include a time-based vesting schedule permitting the options to vest ratably over three years. At December 31, 2017 and 2016, all options were fully vested.

There was no stock-based compensation expense on stock options for all periods presented.

Restricted Stock

Our restricted stock activity and related information are summarized as follows:



	Restricted Stock		Weighted-Average Remaining Contractual Terms (in Years)
Outstanding at January 1, 2015	260,850		3.2
Granted	333,419
Forfeited	(616	)
Outstanding at December 31, 2015	593,653		4.3
Granted	89,384
Forfeited	(5,796	)
Outstanding at December 31, 2016	677,241		3.5
Granted	122,069
Forfeited	(13,601	)
Vested	(237,704	)
Outstanding at December 31, 2017	548,005		0.3
Restricted stock exercisable at December 31, 2017	—

At December 31, 2017, there was $2,383 of unrecognized compensation expense remaining related to our service-based restricted stock awards. The unrecognized compensation cost is expected to be recognized over a weighted average period of 0.3 years. All restricted stock granted prior to May 2014 vested upon our IPO and the remaining grants under the Plan vest six months after the IPO.

Stock-based compensation expense on restricted stock amounted to $3,478, $1,251 and $1,229 for the years ended December 31, 2017, 2016 and 2015, respectively. Due to our limited operating history and lack of marketability, prior to our IPO, discounts of 15%, 15% and 18% were applied when estimating the stock-based compensation for restricted stock in 2017, 2016 and 2015.

Total stock-based compensation expense is included as a component of general and administrative expenses in our statement of operations and was $3,478, $1,251 and $1,229 for the years ended December 31, 2017, 2016 and 2015, respectively. An additional $2,000 of stock-based compensation expense was incurred in 2017 due to the accelerated vesting of restricted shares related to our IPO.

Warrants

For all periods presented, there were warrants issued and outstanding for the issuance of 44,101 shares of common stock. The warrants were issued at exercise prices ranging from $26.27 to $30.97 per share. The warrants generally have a 10-year term. As of December 31, 2017 and 2016, no warrants had been exercised. At inception and as of December 31, 2017 and 2016, no fair value was assigned to the warrants.