Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Disclosures [Abstract]

Fair Value Summary of Long-Term Debt with Fixed Interest Rates

The following table summarizes the fair value of our long-term debt with fixed interest rates, which is estimated based on the published market prices for these debt obligations as of the dates presented:

	December 31, 2013				December 31, 2012
	Fair Value		Carrying Value		Fair Value		Carrying Value
Senior Notes due 2016	$	—	$	—	$	316,500	$	294,759
Senior Notes due 2019	307,500		300,000		286,500		300,000
Senior Notes due 2020	837,969		775,000		—		—
	$	1,145,469	$	1,075,000	$	603,000	$	594,759

Assets and Liabilities Measured at Fair Value on Recurring Basis

The following tables summarize the valuation of those assets and liabilities as of the dates presented:

	As of December 31, 2013
	Fair Value			Fair Value Measurement Classification
Description	Measurement			Level 1			Level 2			Level 3
Assets:
Commodity derivative assets - current	$	3,830		$	—		$	3,830		$	—
Commodity derivative assets - noncurrent	1,552			—			1,552			—
Assets of SERP	3,734			3,734			—			—
Liabilities:
Commodity derivative liabilities - current	—			—			—			—
Commodity derivative liabilities - noncurrent	(10,141		)	—			(10,141		)	—
Deferred compensation - SERP obligation and other	(3,879		)	(3,879		)	—			—

	As of December 31, 2012
	Fair Value			Fair Value Measurement Classification
Description	Measurement			Level 1			Level 2			Level 3
Assets:
Commodity derivative assets - current	$	11,292		$	—		$	11,292		$	—
Commodity derivative assets - noncurrent	5,181			—			5,181			—
Assets of SERP	3,237			3,237			—			—
Liabilities:
Commodity derivative liabilities - current	—			—			—			—
Commodity derivative liabilities - noncurrent	(1,421		)	—			(1,421		)	—
Deferred compensation - SERP obligation and other	(3,305		)	(3,305		)	—			—