Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Percentage of Revenue by Major Customers (Details)

v3.3.1.900
Significant Accounting Policies - Percentage of Revenue by Major Customers (Details) - Sales Revenue Net - Customer Concentration Risk
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Shell Trading (US) Co.      
Entity Wide Revenue Major Customer [Line Items]      
Percentage of receipts 50.00% 47.00% 48.00%
J. P. Morgan      
Entity Wide Revenue Major Customer [Line Items]      
Percentage of receipts 14.00%