Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	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
Investments [Abstract]
Total unrealized gain before federal income taxes	$ 54,565				$ 40,911				$ 54,565	$ 40,911
Deferred tax liability	(19,098)				(14,319)				(19,098)	(14,319)
Net unrealized gains on investments	35,467				26,592				35,467	26,592
Foreign exchange adjustment [Abstract]
Gross unrealized gains	3,039				2,706				3,039	2,706
Deferred tax liability	(1,063)				(947)				(1,063)	(947)
Net unrealized gains on foreign exchange adjustment	1,976				1,759				1,976	1,759
Accumulated other comprehensive income	37,443				28,351				37,443	28,351	35,883
Investments [Abstract]
Pre-tax holding gains (losses) on debt and equity securities arising during period									15,612	(7,146)	11,369
Applicable federal income taxes (credits)									5,464	(2,501)	3,979
Net unrealized gains on investments									10,148	(4,645)	7,390
Pre-tax gains (losses) on debt and equity securities included in net income (loss) during period									1,959	4,088	8,280
Applicable federal income taxes (credits)									686	1,431	2,898
Other comprehensive income (loss), reclassification adjustment for sale of securities included in net income, net of tax									1,273	2,657	5,382
Change in unrealized gains (losses) on investments									8,875	(7,302)	2,008
Reconciliation of Accumulated Other Comprehensive Income [Roll Forward]
Beginning accumulated other comprehensive income				28,351				35,883	28,351	35,883	33,434
Change in foreign exchange adjustment									217	(230)	441
Change in unrealized net gains (losses) on investments									8,875	(7,302)	2,008
Ending accumulated other comprehensive income	37,443				28,351				37,443	28,351	35,883
Retained Earnings (Accumulated Deficit) [Roll Forward]
Beginning retained earnings				241,325				284,346	241,325	284,346	292,543
Net income (loss)	4,676	11,687	4,050	11,506	5,498	(12,971)	(5,504)	(15,198)	31,919	(28,175)	25,015
Dividends									(14,886)	(14,846)	(33,212)
Ending retained earnings	$ 258,358				$ 241,325				$ 258,358	$ 241,325	$ 284,346