Financial Instruments and Fair Value Disclosures (Details Textual) (USD $)	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Financial Instruments and Fair Value Disclosures (Textual) [Abstract]
Allowance for bad debts	$ (5,470,000)	$ (6,867,000)
Net profits interest percent	27.00%
Accounts receivable expected to be collected within one year	50,100,000	95,800,000
Petrobras [Member]
Accounts Receivable By Major Customers [Line Items]
Accounts receivable due from major customer	109,200,000	110,400,000
Percentage of accounts receivable due from major customer	20.00%	20.00%
OGX [Member]
Accounts Receivable By Major Customers [Line Items]
Accounts receivable due from major customer	62,400,000	69,400,000
Percentage of accounts receivable due from major customer	12.00%	12.00%
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	355,600,000	303,900,000
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	$ 975,600,000	$ 902,000,000