Indebtedness - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended		1 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Apr. 30, 2013 7.25% Senior Subordinated notes due 2018
Debt Instrument [Line Items]
Interest capitalized during the period	$ 0		$ 0	$ 0	$ 0
Announced call for redemption amount of debt						250,000,000
Loss on early extinguishment of debt		$ 12,280,000		$ 12,280,000
Debt redemption price percent of par						103.625%
Ratio of debt to EBITDAX	4.25			4.25
Current ratio	1.0			1.0