Legal Proceedings - Additional Information (Detail) (USD $)			0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended			0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2013 Other Litigation Cases	Dec. 31, 2013 Keystone	Jun. 03, 2010 Keystone Slander	Feb. 08, 2010 Keystone Slander	Jun. 03, 2010 Keystone Breach of Contract	Feb. 08, 2010 Keystone Breach of Contract	Nov. 23, 2011 Keystone Exemplary Damages Award	Feb. 12, 2010 Keystone Exemplary Damages Award	Jun. 03, 2010 Keystone Pre-judgment and Post-judgment Interest	Dec. 31, 2013 Keystone Pre-judgment and Post-judgment Interest	Jun. 03, 2010 Keystone Attorneys' Fees	Jun. 03, 2010 Keystone Additional Attorneys' fees	Dec. 31, 2013 Individual Counterparty Other Litigation Cases
Loss Contingencies [Line Items]
Maximum exposure of litigation													$ 150,000
Loss contingency accrual	18,000,000	68,000,000
Estimate of possible losses	50,000,000
Damages awarded			34,300,000	39,000,000	39,000,000	34,300,000	7,500,000	7,500,000	6,800,000	17,000,000	3,500,000	750,000
Escrow reserve		$ 25,000,000