Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2014

Schedule of performance share awards under equity incentive compensation plan

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



	For the Years Ended December 31,
	2014				2013				2012
	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⁾	572,469		$	66.07	669,308		$	63.91	885,894		$	57.52
Granted ⁽¹⁾	202,404		$	94.66	274,831		$	64.13	314,853		$	51.98
Vested ⁽¹⁾	(206,830	)	$	64.79	(345,005	)	$	60.06	(493,679	)	$	44.72
Forfeited ⁽¹⁾	(134,383	)	$	86.72	(26,665	)	$	69.74	(37,760	)	$	65.35
Non-vested at end of year⁽¹⁾	433,660		$	73.63	572,469		$	66.07	669,308		$	63.91

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(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 Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]

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



	For the Years Ended December 31,
	2014				2013				2012
	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	580,431		$	57.05	496,244		$	51.81	308,877		$	44.33
Granted	234,560		$	83.98	329,939		$	60.01	379,332		$	49.47
Vested	(253,031	)	$	58.19	(207,376	)	$	49.73	(166,672	)	$	32.72
Forfeited	(46,236	)	$	62.06	(38,376	)	$	54.37	(25,293	)	$	51.06
Non-vested at end of year	515,724		$	68.29	580,431		$	57.05	496,244		$	51.81

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, 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
For the year ended December 31, 2013
Outstanding, start of year	267,846		$	14.95
Exercised	(228,758	)	$	13.92	$	12,326,994
Forfeited	—		$	—
Outstanding, end of year	39,088		$	20.87	$	2,432,837
Vested and exercisable at end of year	39,088		$	20.87	$	2,432,837
For the year ended December 31, 2014
Outstanding, start of year	39,088		$	20.87
Exercised	(39,088	)	$	20.87	$	1,993,726
Forfeited	—		$	—
Outstanding, end of year	—		$	—	$	—
Vested and exercisable at end of year	—		$	—	$	—

Schedule of employee stock purchase plan

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,
	2014		2013		2012
Risk free interest rate	0.1	%	0.1	%	0.1	%
Dividend yield	0.1	%	0.2	%	0.2	%
Volatility factor of the expected market price of the Company’s common stock	33.0	%	41.1	%	47.8	%
Expected life (in years)	0.5		0.5		0.5

Schedule of net profits plan cash payment allocation

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,
	2014		2013		2012
	(in thousands)
General and administrative expense	$	8,326	$	13,734	$	15,565
Exploration expense	690		1,310		1,751
Total	$	9,016	$	15,044	$	17,316

[1]	(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.