Stock-Based Compensation

We recognized $1.6 million and $2.6 million of stock-based compensation expense during the six months ended June 30, 2016 and 2015, respectively. All stock-based awards granted during the six months ended June 30, 2016 were granted under the 2013 Omnibus Incentive Plan (2013 Plan) or as inducement awards.

Stock Options

Stock options granted under the 2013 Plan or as inducement awards become exercisable in 25% increments on the first four anniversaries of the grant date, and expire on the tenth anniversary of their grant date. Options are granted at an exercise price equal to the market value of the common stock on the grant date. Options granted prior to the 2013 Plan will remain outstanding in accordance with their respective terms.

The following table summarizes all stock option activity for the six months ended June 30, 2016:



	Number of Shares		Weighted- Average Grant- Date Fair Value	Weighted-Average Remaining Contractual Term (Years)
Balance as of December 31, 2015	4,602,746		8.74
Granted	120,371		2.85
Exercised	—		—
Forfeited	(300,332	)	7.54
Vested options expired	(326,134	)	18.47
Balance as of June 30, 2016	4,096,651		7.88	5.93
Exercisable as of June 30, 2016	2,551,045		10.02	3.27

As of June 30, 2016, there was $2.1 million of total unrecognized compensation cost related to unvested stock options. This cost is expected to be recognized over a weighted average period of approximately 2.61 years.

Unvested Shares

Unvested shares granted under the 2013 Plan or as inducement awards vest in three equal increments on the first three anniversaries of their grant date. Unvested shares settle solely in common stock and are treated as equity.

The following table summarizes all unvested share activity for the six months ended June 30, 2016:



	Number of Shares		Weighted- Average Grant- Date Fair Value
Balance as of December 31, 2015	962,446		$	6.57
Granted	690,508		2.71
Vested	(251,505	)	7.70
Forfeited	(122,277	)	7.66
Unvested shares outstanding at June 30, 2016	1,279,172		$	4.16

As of June 30, 2016, there was $4.7 million of total unrecognized compensation cost related to unvested shares. This cost is expected to be recognized over a weighted average period of approximately 2.13 years.

Performance Stock Units

Performance stock units vest in a range between 0% to 100% based upon certain performance criteria in a three year period. At the end of the performance period, the number of shares paid will be based on our performance versus the target. Performance stock units settle solely in common stock and are treated as equity.

The following table summarizes all performance stock unit activity for the six months ended June 30, 2016:



	Number of Shares		Weighted- Average Grant- Date Fair Value
Balance as of December 31, 2015	701,384		$	4.51
Granted	473,000		1.9
Settled	—		—
Forfeited	(197,647	)	6.88
Performance stock units outstanding at June 30, 2016	976,737		$	2.76

As of June 30, 2016, there was $1.5 million of total unrecognized compensation cost related to performance stock units. This cost is expected to be recognized over a weighted average period of approximately 2.66 years.

Phantom Stock Units

During the six months ended June 30, 2016, the Board approved grants of phantom stock units under the 2013 Plan. Units vest in 25% increments on the first four anniversaries of the grant date. Phantom stock units settle solely in cash and are treated as a liability.

The following table summarizes all phantom stock activity for the six months ended June 30, 2016:



	Number of Shares	Weighted- Average Grant- Date Fair Value
Balance as of December 31, 2015	—	$	—
Granted	781,645	2.69
Exercised	—	—
Forfeited	—	—
Phantom stock units outstanding at June 30, 2016	781,645	$	2.69

As of June 30, 2016, there was $1.2 million of total unrecognized compensation cost related to phantom stock. This cost is expected to be recognized over a weighted average period of approximately 3.79 years. Changes in our stock price will result in adjustments to compensation expense and the corresponding liability over the applicable service period.

Cash Performance Stock Units

During the six months ended June 30, 2016, the Board approved grants of cash performance stock units under the 2013 Plan. Cash performance stock units vest in a range between 0% to 100% based upon certain performance criteria measured at December 31, 2018. At the end of the performance period, the number of shares value paid will be based on our performance versus the target. Cash performance stock units settle solely in cash and are treated as a liability.

The following table summarizes all cash performance stock unit activity for the six months ended June 30, 2016:



	Number of Shares	Weighted- Average Grant- Date Fair Value
Balance as of December 31, 2015	—	$	—
Granted	512,127	2.69
Settled	—	—
Forfeited	—	—
Cash performance stock units outstanding at June 30, 2016	512,127	$	2.69

As of June 30, 2016, there was $0.8 million of total unrecognized compensation cost related to cash performance stock units. This cost is expected to be recognized over a weighted average period of approximately 2.63 years. Changes in our stock price and estimated level of performance will result in adjustments to compensation expense and the corresponding liability over the applicable service period.