Financial Instruments and Fair Value Disclosures (Details Textual) (USD $)	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010
Financial Instruments and Fair Value Disclosures (Textual) [Abstract]
Provision for bad debts on trade receivables	$ 8,167,000	$ 31,908,000
Aggregate drilling rate, per day	560,000
Daily payment under amended six-well drilling program	75,000
Receipt of invoice due, in days	due 30 days after receipt of invoice
Remainder of the contractual dayrate	485,000
Net profits interest percent	27.00%
Accounts receivable		49,600,000
Long-term receivable		35,400,000
Total amount payable through the net profits interest	102,700,000	85,000,000
Accounts receivable expected to be collected within one year	102,700,000
Cash held in money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	327,200,000	442,200,000
U.S. Treasury Bills [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	801,500,000	600,000,000
Petrobras [Member]
Accounts Receivable By Major Customers [Line Items]
Accounts receivable due from major customer	143,600,000	180,800,000
Percentage of accounts receivable due from major customer	23.00%	29.00%
OGX [Member]
Accounts Receivable By Major Customers [Line Items]
Accounts receivable due from major customer	$ 62,400,000	$ 52,400,000
Percentage of accounts receivable due from major customer	10.00%	8.00%