Common Stock Common Stock (Tables)

6 Months Ended

Jun. 30, 2022

Equity [Abstract]

Share-based Payment Arrangement, Cost by Plan [Table Text Block]

The following table provides a summary of the impact of our outstanding stock-based compensation plans on the results of operations for the periods presented:

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
	(in thousands)
General and administrative expense	$	6,738	$	6,113	$	11,920	$	10,941
Lease operating expense	558		382		850		574
Total stock-based compensation expense	$	7,296	$	6,495	$	12,770	$	11,515

Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]

The following table presents the changes in non-vested time-based RSUs to eligible employees, including executive officers, for the six months ended June 30, 2022:

	Shares	Weighted Average Grant-Date Fair Value per Share
Non-vested at beginning of period	1,165,187	$	25.33
Granted	344,106	70.58
Vested	(538,750)	25.78
Forfeited	(32,552)	38.87
Non-vested at end of period	937,991	41.21

Restricted Stock Awards, Market-Based, Valuation assumptions [Table Text Block]

The following table summarizes the key assumptions and related information used to determine the grant-date fair value of performance stock units awarded during the periods presented:

	Six Months Ended June 30,
	2022	2021
Expected term of award (in years)	2.9	2.9
Risk-free interest rate	1.7%	0.2%
Expected volatility	86.3%	84.6%
Weighted average grant date fair value per share	$107.85	$54.01

Schedule of Nonvested Performance-based Units Activity [Table Text Block]

The following table presents the change in non-vested market-based awards during the six months ended June 30, 2022:

	Shares	Weighted Average Grant-Date Fair Value per Share
Non-vested at beginning of period	439,229	$	43.21
Granted	102,098	107.85
Granted for performance multiple (1)	241,183	43.10
Released (1)	(241,183)	43.10
Non-vested at end of period	541,327	55.40

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(1) Upon completion of the performance period for the PSUs granted in 2019 and a portion of the PSUs granted in 2020, a performance multiple of 190% was applied to each of the grants resulting in additional grants of PSUs in January 2022.