Investments, Investment Income By Category (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
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income									$ 106,736	$ 90,554	$ 83,425
Investment expenses									(2,995)	(2,907)	(2,686)
Net investment income	$ 27,926	$ 25,939	$ 25,756	$ 24,120	$ 23,956	$ 22,355	$ 21,180	$ 20,156	103,741	87,647	80,739
Total Debt Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income									105,882	89,437	82,168
Equity Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income									208	227	229
Cash Equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income									191	179	353
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income									$ 455	$ 711	$ 675