Stock-Based Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Allocation of Stock-Based Compensation by Functional Category

The following table details the allocation of stock-based compensation to functional expense categories (in thousands):

		Three Months Ended March 31,
		2016		2015
Direct operating expense	$	588	$	886
Brokered natural gas and marketing expense		516		506
Exploration expense		690		732
General and administrative expense		11,113		11,080
Termination costs		¾		1,287
Total stock-based compensation	$	12,907	$	14,491

Summary of Performance Share Unit Awards Activities

The following is a summary of our non-vested PSU awards outstanding at March 31, 2016:

	Number of Units			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2015		262,124		$	64.77
Units granted (a)		118,193			30.47
Units vested		(42,546	)		60.75
Units forfeited		¾			¾
Outstanding at March 31, 2016		337,771		$	53.28

^(a) Amounts granted reflect the number of performance units granted; however, the actual payout of shares will be between zero percent and 150% of the performance units granted depending on the total shareholder return ranking compared to the peer companies at the end of the three-year performance period.

Schedule of Share Based Payment Award Performance Stock Awards Valuation Assumptions

The following assumptions were used to estimate the fair value of PSUs granted during first quarter 2016:

		Three Months Ended March 31,
		2016			2015
Risk-free interest rate		0.85	%		1.05	%
Expected annual volatility		51.7	%		33.9	%
Weighted average grant date fair value per unit	$	30.47		$	55.17

Restricted Stock and Restricted Stock Units Outstanding

The following is a summary of the status of our non-vested restricted stock outstanding at March 31, 2016:

	Equity Awards					Liability Awards
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2015		436,764		$	59.74		308,737		$	65.80
Granted		927,266			28.04		136,275			28.40
Vested		(135,715	)		49.30		(69,683	)		65.22
Forfeited		(30,281	)		50.73		(4,038	)		52.45
Outstanding at March 31, 2016		1,198,034		$	36.61		371,291		$	52.32

Stock Option and SARs Activities

Information with respect to SARs activity is summarized below:

	Shares			Weighted Average Exercise Price
Outstanding at December 31, 2015		1,510,977		$	63.73
Exercised		¾			—
Expired/forfeited		(102,661	)		49.18
Outstanding at March 31, 2016		1,408,316		$	64.79