Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Tax Credit Carryforward [Line Items]
Operating loss carryforward	$ 6,194,192
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	5,384,983
United States [Member]
Tax Credit Carryforward [Line Items]
Operating loss carryforward	542,707
United Kingdom [Member]
Tax Credit Carryforward [Line Items]
Operating loss carryforward	$ 266,502