Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted investments	$ 7,250
Total assets	7,250
Warrants	91,077	[1]	65,193	[1]
Total liabilities	91,077		65,193
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted investments	7,250
Total assets	7,250
Warrants		[1]		[1]
Total liabilities
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted investments
Total assets
Warrants		[1]		[1]
Total liabilities
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted investments
Total assets
Warrants	91,077	[1]	65,193	[1]
Total liabilities	$ 91,077		$ 65,193

[1] See Note 5 for additional information related to the determination of fair value of warrants and a reconciliation of changes in fair value.