Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments [Abstract]
Total unrealized gain before federal income taxes	$ 75,521				$ 54,565				$ 75,521	$ 54,565
Deferred tax liability	(26,432)				(19,098)				(26,432)	(19,098)
Net unrealized gains on investments	49,089				35,467				49,089	35,467
Foreign exchange adjustment [Abstract]
Gross unrealized gains	2,155				3,039				2,155	3,039
Deferred tax liability	(754)				(1,063)				(754)	(1,063)
Net unrealized gains on foreign exchange adjustment	1,401				1,976				1,401	1,976
Accumulated other comprehensive income	50,490				37,443				50,490	37,443	28,351
Investments [Abstract]
Pre-tax holding gains (losses) on debt and equity securities arising during period									36,477	15,612	(7,146)
Applicable federal income taxes (credits)									12,766	5,464	(2,501)
Net unrealized gains on investments									23,711	10,148	(4,645)
Pre-tax gains on debt and equity securities included in net income during period									15,520	1,959	4,088
Less: applicable federal income taxes									5,431	686	1,431
Other comprehensive income (loss), reclassification adjustment for sale of securities included in net income, net of tax									10,089	1,273	2,657
Change in unrealized gains (losses) on investments									13,622	8,875	(7,302)
Reconciliation of Accumulated Other Comprehensive Income [Roll Forward]
Beginning accumulated other comprehensive income				37,443				28,351	37,443	28,351	35,883
Change in foreign exchange adjustment									(575)	217	(230)
Change in unrealized net gains (losses) on investments									13,622	8,875	(7,302)
Ending accumulated other comprehensive income	50,490				37,443				50,490	37,443	28,351
Retained Earnings (Accumulated Deficit) [Roll Forward]
Beginning retained earnings				258,358				241,325	258,358	241,325	284,346
Net income (loss)	8,967	7,771	4,907	14,943	4,676	11,687	4,050	11,506	36,588	31,919	(28,175)
Dividends									(14,943)	(14,886)	(14,846)
Ending retained earnings	$ 280,003				$ 258,358				$ 280,003	$ 258,358	$ 241,325