Derivative Instruments and Hedging Activities - Additional Information (Detail)	Dec. 31, 2013 Counterparty
Derivative [Line Items]
Number of counterparties	14
Fixed-Price Swaps [Member] \| 2014 [Member] \| Nymex Henry Hub [Member] \| Derivatives Not Designated as Cash Flow Hedging Instruments [Member] \| Open Natural Gas Derivative Positions [Member]
Derivative [Line Items]
Open positions	55,900,000
Weighted average fixed price	4.35

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant