Reconciliation of Change in Value of Warrants Recorded as Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class of Warrant or Right [Line Items]
Balance at beginning of year	$ 5,446	$ 39,111	$ 27,609
Change in value of warrants	91,938	(33,022)	11,502
Issuances	0	0	0
Balance at end of year	65,193	5,446	39,111
Warrant
Class of Warrant or Right [Line Items]
Reclassification to shareholders' equity upon exercise of warrants	$ (32,191)	$ (643)	$ 0