Unaudited Quarterly Financial Data (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Unaudited Quarterly Financial Data [Abstract]
Net premiums written	$ 260,736,000	[1]	$ 263,505,000		$ 238,605,000		$ 254,986,000		$ 263,773,000		$ 255,745,000		$ 270,399,000		$ 274,463,000		$ 1,017,832,000		$ 1,064,380,000		$ 1,101,795,000
Net premiums earned	261,705,000	[1]	266,432,000		242,628,000		262,405,000		275,741,000		275,094,000		284,454,000		288,546,000		1,033,170,000		1,123,835,000		1,168,747,000
Investment income, net of expenses	21,660,000	[1]	30,394,000		32,178,000		37,408,000		40,339,000		48,898,000		55,490,000		56,543,000		121,640,000		201,270,000		247,253,000
Loss incurred, net	688,636,000	[1]	490,121,000		551,408,000		337,088,000		482,070,000		462,654,000		459,552,000		310,431,000		2,067,253,000		1,714,707,000		1,607,541,000
Change in premium deficiency reserve (note 10)	(10,351,000)	[1]	(9,144,000)		(27,358,000)		(14,183,000)		(11,709,000)		(12,388,000)		(11,035,000)		(9,018,000)		(61,036,000)		(44,150,000)		(51,347,000)
Underwriting and other operating expenses	51,516,000	[1]	50,678,000		48,910,000		50,343,000		50,680,000		52,477,000		54,043,000		57,550,000		201,447,000		214,750,000
Interest expense	25,327,000	[1]	24,478,000		24,912,000		24,627,000		25,142,000		25,761,000		26,326,000		26,042,000		99,344,000		103,271,000		98,589,000
Net income (loss)	(386,691,000)	[1]	(246,942,000)		(273,891,000)		(19,555,000)		(135,294,000)		(165,205,000)		(151,732,000)		(33,661,000)		(927,079,000)		(485,892,000)		(363,735,000)
Income (loss) per share [Abstract]
Basic	$ (1.91)	[1],[2]	$ (1.22)	[2]	$ (1.36)	[2]	$ (0.1)	[2]	$ (0.67)	[1],[2]	$ (0.82)	[2]	$ (0.75)	[2]	$ (0.17)	[2]	$ (4.59)	[2]	$ (2.42)	[2]	$ (2.06)
Diluted	$ (1.91)	[1],[2]	$ (1.22)	[2]	$ (1.36)	[2]	$ (0.1)	[2]	$ (0.67)	[1],[2]	$ (0.82)	[2]	$ (0.75)	[2]	$ (0.17)	[2]	$ (4.59)	[2]	$ (2.42)	[2]	$ (2.06)
Obligations under the Disputed Policies																	267,500,000
Increase in loss reserves for the probable settlement agreements																	$ 100,000,000

[1] The results for the fourth quarter of 2012 include a loss of approximately $267 million related to our settlement with Freddie Mac and approximately $100 million related to our probable rescission settlement agreements. See Note 20 - "Litigation and Contingencies".

[2] Due to the use of weighted average shares outstanding when calculating earnings per share, the sum of the quarterly per share data may not equal the per share data for the year.