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Financial Instruments - Schedule of Changes in Fair Value of Financial Assets and Liabilities Classified as Level 3 (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Net assets (liabilities) at beginning of period $ 16,757 $ (865)
Total realized and unrealized gains (losses):    
Included in earnings 3,966 17,420
Included in other comprehensive income (loss) 137 48
Purchases, sales, issuances and settlements (20,867) 154
Net assets (liabilities) at end of period $ (7) $ 16,757