Long-Term Debt (Revolving Credit Facility - Narrative) (Details) (USD $)					1 Months Ended	12 Months Ended					12 Months Ended							12 Months Ended
	Dec. 31, 2013 Letters Of Credit [Member]		Dec. 31, 2012 Letters Of Credit [Member]		Jul. 31, 2012 Senior Secured Revolving Credit Facility [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] item	Oct. 15, 2013 Senior Secured Revolving Credit Facility [Member]	Jan. 15, 2013 Senior Secured Revolving Credit Facility [Member]	Oct. 30, 2012 Senior Secured Revolving Credit Facility [Member]	Apr. 30, 2012 Senior Secured Revolving Credit Facility [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Forecasted Production In Current Year Attributable To Proved Developed Producing Reserves And Reserves To Be Acquired [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Forecasted Production For The Next Two Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Forecasted Production For Three Plus Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Base Rate [Member] Interest Rate Option 1 [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Interest Rate Option 1 [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Letters Of Credit [Member]	Jan. 15, 2013 Senior Secured Revolving Credit Facility [Member] Letters Of Credit [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Minimum [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Minimum [Member] Interest Rate Option 1 [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Minimum [Member] London Interbank Offered Rate (LIBOR) [Member] Interest Rate Option 2 [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Maximum [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Maximum [Member] Interest Rate Option 1 [Member]	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member] Maximum [Member] London Interbank Offered Rate (LIBOR) [Member] Interest Rate Option 2 [Member]
Debt Instrument [Line Items]
Credit Agreement, initiation date						Dec. 22, 2010
Credit Agreement, current borrowing capacity					$ 655,000,000	$ 950,000,000	$ 950,000,000	$ 900,000,000		$ 730,000,000							$ 30,000,000
Credit Agreement, amount outstanding	23,488,000	[1]	23,488,000	[1]		615,000,000										23,500,000
Credit Agreement, remaining borrowing capacity						311,500,000
Credit Agreement, interest rate during period including the impact of hedges						3.60%
Credit Agreement, interest rate at end of period excluding potential impact of hedges						2.20%
Credit Agreement, prior maximum borrowing capacity										750,000,000
Credit Agreement, maximum borrowing capacity						1,500,000,000			730,000,000	1,500,000,000
Credit Agreement, prior current borrowing capacity					730,000,000			730,000,000		630,000,000							20,000,000
Credit Agreement, prior expiration date						Dec. 22, 2015
Credit Agreement, expiration date						Apr. 20, 2017
Credit Agreement, reduction in borrowing capacity					75,000,000
Credit Agreement, write-off of deferred loan costs					$ 700,000
Credit Agreement, term						5 years
Credit Agreement, interest rate description						Borrowings bear interest at our option of either (i) the greater of the prime rate of Wells Fargo Bank, National Association, the federal funds effective rate plus 0.50%, or the one-month adjusted LIBOR plus 1.0%, all of which would be subject to a margin that varies from 0.50% to 1.50% per annum according to the borrowing base usage (which is the ratio of outstanding borrowings and letters of credit to the borrowing base then in effect), or (ii) the applicable LIBOR plus a margin that varies from 1.50% to 2.50% per annum according to the borrowing base usage.
Credit Agreement, basis spread on variable rate														0.50%	1.00%				0.50%	1.50%		1.50%	2.50%
Percentage multiplied by stated principal amount of debt issuance to reduce borrowing base						0.25
Percentage of oil and gas properties collateralized by liens																		80.00%
Credit Agreement, unused portion, commitment fee percentage																		0.375%			0.50%
Total debt to EBITDAX ratio to be maintained for Credit Agreement						4.0
Current ratio to be maintained for Credit Agreement						1.0
Number of days after fiscal year end to provide audited financial statements for credit agreement						90 days
Number of days after fiscal quarter end to provide unaudited financial statements for credit agreement						45 days
Percentage of forecasted production prohibiting entering into derivative contracts											90.00%	85.00%	75.00%

[1] These letters of credit relate to a reclamation deposit requirement. Refer to Note 11 - Commitments and Contingencies for details.