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Acquisition of SPT - Summarized Consolidated Pro forma Financial Information (Detail) - Ship to Ship Transfer Business
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
USD ($)
$ / shares
Business Acquisition [Line Items]  
Revenues | $ $ 570,381
Net income | $ $ 178,266
Earnings per common share:  
Basic (in dollars per share) | $ / shares $ 1.33
Diluted (in dollars per share) | $ / shares $ 1.33