Common Stock Common Stock (Tables)

9 Months Ended

Sep. 30, 2021

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 September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
	(in thousands)
General and administrative expense	$	5,479	$	5,171	$	16,420	$	16,632
Lease operating expense	300		234		874		809
Total stock-based compensation expense	$	5,779	$	5,405	$	17,294	$	17,441

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 all employees, including executive officers, for the nine months ended September 30, 2021:

	Shares	Weighted-Average Grant Date Fair Value per Share
Non-vested at beginning of period	1,150,970	$	20.14
Granted	647,453	33.48
Vested	(531,759)	25.04
Forfeited	(82,693)	22.36
Non-vested at end of period	1,183,971	25.08

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:

	Nine Months Ended September 30,
	2021	2020
Expected term of award (in years)	3	3
Risk-free interest rate	0.2%	1.4%
Expected volatility	84.6%	46.6%
Weighted-average grant date fair value per share	$54.01	$33.52

The fair value of the SRC PSU awards was determined on the grant date of January 13, 2020 using the Monte Carlo pricing model using the following assumptions:

	Nine Months Ended September 30, 2020
Expected term of awards (in years)	2
Risk-free interest rate	1.6%
Expected volatility	56.9%
Weighted-average grant date fair value per share	$33.35

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

The following table presents the change in non-vested market-based awards, including SRC PSUs, during the nine months ended September 30, 2021:

	Shares	Weighted-Average Grant Date Fair Value per Share
Non-vested at beginning of period	499,547	$	38.66
Granted	207,655	54.01
Non-vested at end of period	707,202	43.17