Fair Value Measurements (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Assets measured at fair value on a recurring basis
Total fixed maturity	$ 796,348,000	$ 815,999,000
Equities securities	9,812,000
Short-term investments	97,531,000	57,417,000
Trading securities	4,935,000
Total	908,626,000
Quoted Prices in Active Markets for Identical Level 1 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	23,232,000
Equities securities	3,106,000
Short-term investments	97,531,000
Trading securities	344,000
Total	124,213,000
Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	773,116,000
Trading securities	4,591,000
Total	777,707,000
Significant Unobservable Inputs Level 3 [Member]
Assets measured at fair value on a recurring basis
Equities securities	6,706,000
Total	6,706,000
U.S. Treasury securities and other government corporations and agencies [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	52,082,000	63,090,000
U.S. Treasury securities and other government corporations and agencies [Member] | Quoted Prices in Active Markets for Identical Level 1 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	23,232,000
U.S. Treasury securities and other government corporations and agencies [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	28,850,000
States of the U.S. and political subdivisions of the states [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	33,222,000	32,257,000
States of the U.S. and political subdivisions of the states [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	33,222,000
Corporate securities [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	331,396,000	326,926,000
Corporate securities [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	331,396,000
Mortgage-backed securities [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	258,593,000	270,811,000
Mortgage-backed securities [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	258,592,000
Commercial mortgage-backed securities [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	63,493,000	63,961,000
Commercial mortgage-backed securities [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	63,493,000
Asset-backed securities [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	57,562,000	58,954,000
Asset-backed securities [Member] | Significant Other Significant Other Level 2 [Member]
Assets measured at fair value on a recurring basis
Total fixed maturity	$ 57,563,000