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, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net liabilities at beginning of period	$ (865)
Total realized and unrealized gains / losses
Included in earnings	(8,854)
Included in other comprehensive loss	(50)
Purchases, sales, issuances and settlements	2,854
Net liabilities at end of period	$ (6,915)