CONCENTRATION OF MARKET AND CREDIT RISK (Schedule of Revenue by Major Customers) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Revenue, Major Customer [Line Items]
Revenues from significant customers	$ 292,721	[1]	$ 272,688	[1]	$ 253,161	[1]	$ 245,093	[1]	$ 252,525	[1]	$ 178,603	[1]	$ 171,621	[1]	$ 184,672	[1]	$ 1,063,663	$ 787,421	$ 645,076
Chevron Australia Pty. Ltd. [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	197,242	265,731	199,685
Apache Energy Ltd. [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	159,369	0	0
Hess Corporation [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	154,973	0	0
Noble Energy Inc. [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	153,615	137,135	0
Sarawak Shell Bhd. [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	0	44,405	138,836
Kosmos Energy Ghana Inc. [Member]
Revenue, Major Customer [Line Items]
Revenues from significant customers																	$ 0	$ 90,088	$ 136,205

[1] The sum of the individual quarterly net income per common share amounts may not agree with year-to-date net income per common share as each quarterly computation is based on the weighted average number of common shares outstanding during that period.