Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Tax Credit Carryforward [Line Items]
Operating loss carryforward	$ 6,031,251
Expiration period	Expiring in 2029 and will fully expire in 2034
Operating tax carryforward expiration year start	2029
Operating tax carryforward expiration year end	2034
U. S. Federal Net Operating Tax [Member]
Tax Credit Carryforward [Line Items]
Net operating tax carryforward	5,096,774
United States [Member]
Tax Credit Carryforward [Line Items]
Operating loss carryforward	623,446
United Kingdom [Member]
Tax Credit Carryforward [Line Items]
Operating loss carryforward	$ 311,031