Investments (Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investments [Line Items]
Total investment income	$ 143,511	$ 146,193	$ 147,247
Less: Investment expense	2,564	2,379	2,298
Net investment income	140,947	143,814	144,949
Parent Company [Member]
Investments [Line Items]
Net investment income	1,411	951	1,127
Fixed Maturity Securities [Member]
Investments [Line Items]
Total investment income	130,895	136,345	137,607
Equity Securities [Member]
Investments [Line Items]
Total investment income	10,869	8,435	8,558
Short-Term Investments [Member]
Investments [Line Items]
Total investment income	$ 1,747	$ 1,413	$ 1,082