Our 2018 Equity Incentive Plan (the “Plan”) was approved by stockholders in May 2018. The Plan authorizes us to issue up to 4.35 million shares of common stock, along with non-qualified stock options, stock appreciation rights, restricted stock and performance units to our officers, key employees, non-employee directors and consultants. At June 30, 2020, there were 73 thousand shares available for future grants under this Plan. No more than 1.2 million shares may be used under the Plan as “full value” awards, which include restricted stock and performance units. It is our policy to issue shares from authorized but not issued shares upon the exercise of stock options.

Under the terms of the Plan, each year eligible participants are granted time value restricted stock units (“RSUs”), vesting ratably over a three-year period, and performance restricted stock units (“PSUs”), with three-year cliff vesting. Upon vesting, each restricted stock award is exchangeable for one share of the Company’s common stock, with accrued dividends.

On May 16, 2019 the Company granted the following equity awards to our then new President and Chief Executive Officer in connection with the 2019 Inducement Grant Plan (the “Inducement Plan”): (i) an initial award consisting of (a) 666,667 PSUs at target, vesting in three approximately equal installments, to the extent the performance metrics are satisfied, during each of three performance periods and (b) 333,333 RSUs, vesting in approximately equal installments on February 28, 2020, 2021 and 2022; (ii) a 2019-2021 PSU grant, with the target number of 316,832 PSUs, which will vest to the extent the performance metrics are satisfied; and (iii) a 2019 RSU grant of 158,416 RSUs, vesting in approximately equal installments on February 28, 2020, 2021 and 2022. The PSU awards may be earned at up to 200% of target depending on the level of achievement of the performance metrics.

Restricted stock unit and restricted performance stock unit activity for the six months ended June 30, 2020 is summarized in the following table:

	Equity Incentive Awards
	Restricted Stock Units			Weighted Average Grant Date Fair Value		Performance Shares			Weighted Average Grant Date Fair Value		Options			Weighted Average Exercise Price
Balance at December 31, 2019		1,047,256		$	5.39		1,548,793		$	7.17		50,250		$	18.86
Granted		634,317			2.87		948,636			3.25		—			—
Settled		(401,723	)		6.14		(245,713	)		5.05		—			—
Forfeited or expired		(7,776	)		4.78		(44,827	)		20.95		(23,250	)		16.81
Balance at June 30, 2020		1,272,074		$	3.90		2,206,889		$	5.33		27,000		$	20.63

Vested or expected to vest at June 30, 2020		1,122,573		$	3.88		361,278		$	7.74		27,000		$	20.63

Stock-based compensation expense was $0.9 million and $1.4 million for the three-month periods ended June 30, 2020 and 2019, respectively. Stock-based compensation expense was $0.7 million and $1.9 million for the six-month periods ended June 30, 2020 and 2019, respectively. The year-over-year reduction in expense is due to the reduction of our estimates regarding the achievement of the performance metric, to zero, in light of the global pandemic. This change in estimate resulted in a reversal of $1.2 million of previously accrued expense in the first quarter of 2020. Unrecognized stock-based compensation expense related to non-vested awards of $5.1 million is expected to be recognized over a weighted average period of approximately 1.8 years as of June 30, 2020.