Investments (Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments [Line Items]
Total investment income	$ 135,461	$ 143,511	$ 146,193
Less: Investment expense	(3,565)	(2,564)	(2,379)
Net investment income	131,896	140,947	143,814
Fixed Maturity Securities [Member]
Investments [Line Items]
Total investment income	117,557	130,895	136,345
Equity Securities [Member]
Investments [Line Items]
Total investment income	15,831	10,869	8,435
Short-Term Investments [Member]
Investments [Line Items]
Total investment income	$ 2,073	$ 1,747	$ 1,413