Income Taxes (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2007	Dec. 31, 2012
Tax provision (benefit) [Abstract]
Benefit from income taxes	$ (21,590,000)	$ (6,062,000)
Change in valuation allowance	22,729,000	7,425,000
Provision for income taxes	1,139,000	1,363,000
Increase (decrease) in deferred tax valuation allowance, included in other comprehensive income, due to change in deferred tax liability related to unrealized gains/losses on investments	3,000,000	15,200,000
Valuation allowance	991,700,000			966,000,000
Net operating loss carryforwards, regular tax basis	2,600,000,000
Net operating loss carryforwards for computing the alternative minimum tax	1,700,000,000
Information regarding income tax examinations [Abstract]
Amount of IRS assessment for unpaid taxes and penalties related to REMIC issue			190,700,000
Amount of payment made related to the IRS assessment on the REMIC issue			$ 65,200,000