Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement [Line Items]
Net investment income earned	$ 30,108	$ 32,061	$ 32,230	$ 26,917	$ 32,108	$ 34,292	$ 36,774	$ 35,534	$ 121,316	$ 138,708	$ 134,643
Fixed Income Securities [Member]
Statement [Line Items]
Net investment income earned									123,230	126,489	121,582
Equity Securities, Dividend Income [Member]
Statement [Line Items]
Net investment income earned									9,161	7,449	6,140
Short-term Investments [Member]
Statement [Line Items]
Net investment income earned									112	66	117
Other Investment Portfolio [Member]
Statement [Line Items]
Net investment income earned									(1,890)	13,580	15,208
Investment Expenses [Member]
Statement [Line Items]
Net investment income earned									$ (9,297)	$ (8,876)	$ (8,404)