Compensation Plans (Tables)

6 Months Ended

Jun. 30, 2011

Compensation Plans.

Schedule of performance share awards under equity incentive compensation plan

			Weighted-
			Average Grant-
	PSAs		Date Fair Value
Non-vested, at January 1, 2011	1,110,666		$	39.48
Granted	—		$	—
Vested (1)	(7,682	)	$	36.69
Forfeited	(23,289	)	$	39.41
Non-vested, at June 30, 2011	1,079,695		$	39.50

(1) The number of awards vested assumes a multiplier of one. The final number of shares vested may vary depending on the ending three-year multiplier, which ranges from zero to two.

Schedule of restricted stock unit incentive program under equity incentive compensation plan

			Weighted-Average
			Grant-Date
	RSUs		Fair Value
Non-vested, at January 1, 2011	333,359		$	31.16
Granted	8,287		$	60.33
Vested	(27,714	)	$	37.84
Forfeited	(6,638	)	$	29.88
Non-vested, at June 30, 2011	307,294		$	31.37

Schedule of stock option grants under prior stock option plans

			Weighted-
			Average		Aggregate
	Options		Exercise Price		Intrinsic Value
Outstanding, January 1, 2011	920,765		$	13.11	$	42,192,057
Exercised	(310,412	)	$	12.26
Forfeited	—		$	—
Outstanding, June 30, 2011	610,353		$	13.54	$	36,586,971
Vested and exercisable, June 30, 2011	610,353		$	13.54	$	36,586,971

Summary of cash payments made or accrued under the Net Profits Plan

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2011		2010		2011		2010
	(in thousands)
General and administrative expense	$	5,261	$	5,381	$	10,591	$	12,315
Exploration expense	585		667		1,062		1,258
Total	$	5,846	$	6,048	$	11,653	$	13,573