Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2015

Stock Compensation Plans [Line Items]

Schedule of stock-based compensation costs

Stock-based compensation costs for the years ended December 31, 2015, 2014 and 2013, are as follows:

	Year Ended December 31,
In thousands	2015		2014		2013
Stock-based compensation expensed
General and administrative expenses	$	27,995	$	27,789	$	30,429
Lease operating expenses	2,609		2,724		2,574
Total stock-based compensation expensed	30,604		30,513		33,003
Stock-based compensation capitalized	8,681		9,019		9,088
Total cost of stock-based compensation arrangements	$	39,285	$	39,532	$	42,091
Income tax benefit recognized for stock-based compensation arrangements	$	11,630	$	11,595	$	12,541

Schedule of SARs valuation assumptions

	Year Ended December 31,
	2015			2014			2013
Weighted average fair value of SARs granted	$	1.77		$	3.55		$	6.72
Risk-free interest rate	1.29		%	1.31		%	0.67		%
Expected life	4.0 years			3.8 to 4.0 years			3.6 to 4.8 years
Expected volatility	39.4		%	38.0		%	50.4		%
Dividend yield	3.42		%	3.10		%	—		%

Summary of stock option and SARs activity

The following is a summary of our stock option and SAR activity:

	Number of Awards		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2014	7,468,733		$	16.90
Granted	3,509,159		7.30
Exercised	(74,660	)	7.58
Forfeited	(599,256	)	9.74
Expired	(1,400,462	)	16.37
Outstanding at December 31, 2015	8,903,514		13.76		3.3	$	—
Exercisable at end of period	5,214,820		$	17.40	1.5	$	—

Disclosure of intrinsic value of stock options exercised and grant-date fair value of awards vested

The following is a summary of the total intrinsic value of stock options and SARs exercised and grant-date fair value of stock options and SARs vested:

	Year Ended December 31,
In thousands	2015		2014		2013
Intrinsic value of stock options and SARs exercised	$	60	$	7,985	$	17,287
Grant-date fair value of stock options and SARs vested	6,534		9,998		12,852

Summary of cash received from stock option exercises

The following is a summary of cash received from stock option exercises under share-based payment arrangements and tax benefits realized from the exercises of stock options and SARs:

	Year Ended December 31,
In thousands	2015		2014		2013
Cash received from stock option exercises	$	562	$	7,022	$	5,487
Tax benefit realized for the exercises of stock options and SARs	—		212		437

Restricted Stock [Member]

Stock Compensation Plans [Line Items]

Summary of the total vesting date fair value of non-performance-based restricted stock and performance-based awards

The following is a summary of the total vesting date fair value of non-performance-based restricted stock:

	Year Ended December 31,
In thousands	2015		2014		2013
Fair value of restricted stock vested	$	12,549	$	24,780	$	21,529

Summary of non-performance-based restricted stock activity

A summary of the status of our nonvested non-performance-based restricted stock grants issued, and the changes during the year ended December 31, 2015, is presented below:

	Number of Shares		Weighted Average Grant-Date Fair Value
Nonvested at December 31, 2014	3,739,034		$	16.17
Granted	4,441,936		6.73
Vested	(1,718,669	)	16.67
Forfeited	(872,614	)	11.30
Nonvested at December 31, 2015	5,589,687		9.27

Performance equity awards [Member]

Stock Compensation Plans [Line Items]

Schedule of nonvested performance-based Units Activity

A summary of the status of the nonvested performance-based equity awards (presented at the target level) during the year ended December 31, 2015, is as follows:

	Performance-Based Operational Awards				Performance-Based TSR Awards
	Number of Awards		Weighted Average Grant-Date Fair Value		Number of Awards		Weighted Average Grant-Date Fair Value
Nonvested at December 31, 2014	451,398		$	16.65	533,611		$	20.66
Granted (1)	519,279		7.31		519,279		7.59
Vested (2)	(280,575	)	7.73		(82,213	)	7.29
Forfeited	(130,842	)	10.79		(202,122	)	14.98
Nonvested at December 31, 2015	559,260		13.82		768,555		14.75

(1) Amounts granted reflect the number of performance units granted. The actual payout of the shares may be between 0% and 200% of the performance units granted.

(2) During 2015, the service period lapsed on these performance unit awards. The lapsed units earned a weighted average of 135% and 50% of target for each vested performance-based operational and TSR award, respectively, representing 413,232 aggregate shares of common stock issued.

Performance-based TSR Awards [Member]

Stock Compensation Plans [Line Items]

Summary of Performance-Based TSR Awards Valuation Assumptions

The range of assumptions used in the Monte Carlo simulation valuation approach for Performance-Based TSR Awards (presented at the target level) are as follows:

	Year Ended December 31,
	2015			2014			2013
Weighted average fair value of Performance-Based TSR Awards granted	$	7.59		$	19.81		$	20.08
Risk-free interest rate	0.96		%	0.80		%	0.41		%
Expected life	3.0 years			3.0 years			3.0 years
Expected volatility	33.6		%	39.4		%	42.3		%
Dividend yield	3.42		%	2.50		%	—		%

Performance-based Operational Award [Member]

Stock Compensation Plans [Line Items]

Summary of the total vesting date fair value of non-performance-based restricted stock and performance-based awards

The following is a summary of the total vesting date fair value of performance-based equity awards:

	Year Ended December 31,
In thousands	2015		2014		2013
Vesting date fair value of Performance-Based Operational Awards	$	2,861	$	—	$	2,541
Vesting date fair value of Performance-Based TSR Awards	300		—		—