Significant Accounting Policies - Immaterial Restatement - Narrative (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Total other-than-temporary impairment losses	$ (2,713)	$ (78,950)	$ (47,264)	$ (161,924)
Portion of loss recognized in other comprehensive income (loss)	(7,301)	(71,610)	(76,801)	(83,989)
Previously Reported [Member]
Total other-than-temporary impairment losses		(151,300)		(293,900)
Portion of loss recognized in other comprehensive income (loss)		728		48,000
Restated Account Adjustment [Member]
Total other-than-temporary impairment losses		72,400		132,000
Portion of loss recognized in other comprehensive income (loss)		$ (72,400)		$ (132,000)