Financial Instruments, Fair Value Measurements and Credit Risk - Contingent Consideration and Liability (Details) (Ecopetrol Dispute [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Ecopetrol Dispute [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	$ 7,586	$ 0
Foreign currency derivative liability	3,057	0
Contingent consideration liability (Note 4)	1,061	1,061
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 4,118	$ 1,061