Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2012

Schedule of performance share awards under equity incentive compensation plan

A summary of the status and activity of PSUs is presented in the following table:



	For the Years Ended December 31,
	2012				2011				2010
	PSUs		Weighted-Average Grant-Date Fair Value		PSUs		Weighted-Average Grant-Date Fair Value		PSUs		Weighted-Average Grant-Date Fair Value
Non-vested at beginning of year⁽¹⁾	885,894		$	57.52	1,110,666		$	39.48	1,069,090		$	32.52
Granted⁽¹⁾	314,853		$	51.98	266,282		$	91.45	387,651		$	52.35
Vested⁽¹⁾	(493,679	)	$	44.72	(364,172	)	$	35.74	(210,801	)	$	31.18
Forfeited⁽¹⁾	(37,760	)	$	65.35	(126,882	)	$	33.32	(135,274	)	$	34.28
Non-vested at end of year⁽¹⁾	669,308		$	63.91	885,894		$	57.52	1,110,666		$	39.48


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

^[1]

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

A summary of the status and activity of non-vested RSUs is presented below:



	For the Years Ended December 31,
	2012				2011				2010
	RSUs		Weighted- Average Grant-Date Fair Value		RSUs		Weighted- Average Grant-Date Fair Value		RSUs		Weighted- Average Grant-Date Fair Value
Non-vested at beginning of year	308,877		$	44.33	333,359		$	31.16	407,123		$	34.67
Granted	379,332		$	49.47	98,952		$	72.69	128,865		$	40.31
Vested	(166,672	)	$	32.72	(105,820	)	$	30.61	(160,398	)	$	46.30
Forfeited	(25,293	)	$	51.06	(17,614	)	$	36.80	(42,231	)	$	35.43
Non-vested at end of year	496,244		$	51.81	308,877		$	44.33	333,359		$	31.16

Schedule of stock option grants under prior stock option plans

A summary of activity associated with the Company’s Stock Option Plans during the last three years is presented in the following table:



			Weighted -
			Average		Aggregate
			Exercise		Intrinsic
	Shares		Price		Value
For the year ended December 31, 2010
Outstanding, start of year	1,274,920		$	13.31
Exercised	(346,377	)	$	13.77	$	11,281,865
Forfeited	(7,778	)	$	16.66
Outstanding, end of year	920,765		$	13.11	$	42,192,057
Vested and exercisable at end of year	920,765		$	13.11	$	42,192,057
For the year ended December 31, 2011
Outstanding, start of year	920,765		$	13.11
Exercised	(412,551	)	$	12.19	$	24,359,240
Forfeited	—		$	—
Outstanding, end of year	508,214		$	13.86	$	30,109,110
Vested and exercisable at end of year	508,214		$	13.86	$	30,109,110
For the year ended December 31, 2012
Outstanding, start of year	508,214		$	13.86
Exercised	(240,368	)	$	12.65	$	11,842,575
Forfeited	—		$	—
Outstanding, end of year	267,846		$	14.95	$	9,983,177
Vested and exercisable at end of year	267,846		$	14.95	$	9,983,177

Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding [Table Text Block]

A summary of additional information related to options outstanding as of December 31, 2012, follows:



		Options Outstanding and Exercisable
		Number	Weighted-
		Of Options	Average
		Outstanding	Remaining
Exercise		and	Contractual
Price⁽¹⁾		Exercisable	Life
$	12.53	33,805	0.25 years
$	12.66	28,053	0.75 years
$	13.39	17,142	0.81 years
$	13.65	35,893	0.50 years
$	14.25	104,093	1 year
$	20.87	48,860	2 years
Total		267,846

(1) Exercise price is equal to the weighted average exercise price.

^[1],[2]

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

The fair value of ESPP shares issued during the periods reported were estimated using the following weighted-average assumptions:



	For the Years Ended December 31,
	2012		2011		2010
Risk free interest rate	0.1	%	0.2	%	0.2	%
Dividend yield	0.2	%	0.2	%	0.3	%
Volatility factor of the expected market
price of the Company’s common stock	47.8	%	36.3	%	46.3	%
Expected life (in years)	0.5 years		0.5 years		0.5 years

Schedule of Net Profits Plan Cash Payment Allocation [Table Text Block] [Table Text Block]

Cash payments made or accrued under the Net Profits Plan that have been recorded as either general and administrative expense or exploration expense are detailed in the table below:



	For the Years Ended December 31,
	2012		2011		2010
	(in thousands)
General and administrative expense	$	15,565	$	19,326	$	19,798
Exploration expense	1,751		2,091		2,633
Total	$	17,316	$	21,417	$	22,431

[1]	The number of awards assumes a one multiplier. The final number of shares of common stock issued may vary depending on the ending three-year performance multiplier, which ranges from zero to two.
[2]	Exercise price is equal to the weighted average exercise price.