Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 Year Contract
Commitments And Contingencies Disclosure [Line Items]
Number of drilling rigs used under drilling contracts	3
Maximum period of drilling contracts in years	4
Maximum penalties on early termination of drilling contracts	$ 30.0
Two Thousand And Twelve [Member]
Commitments And Contingencies Disclosure [Line Items]
Drilling contracts future minimum commitments	5.9
Two Thousand And Thirteen [Member]
Commitments And Contingencies Disclosure [Line Items]
Drilling contracts future minimum commitments	23.2
Two Thousand And Fourteen [Member]
Commitments And Contingencies Disclosure [Line Items]
Drilling contracts future minimum commitments	9.9
Two Thousand And Fifteen [Member]
Commitments And Contingencies Disclosure [Line Items]
Drilling contracts future minimum commitments	$ 2.2