Investments, Major Categories of Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment Income, Net [Abstract]
Investment Income	$ 25,001	$ 20,422	$ 16,980
Investment expenses	(2,953)	(2,327)	(2,497)
Net investment income	22,048	18,095	14,483
Interest on Fixed Income Securities [Member]
Investment Income, Net [Abstract]
Investment Income	19,092	15,340	13,254
Dividends on Equity Securities [Member]
Investment Income, Net [Abstract]
Investment Income	4,380	4,611	3,598
Money Market Funds, Short term and Other [Member]
Investment Income, Net [Abstract]
Investment Income	$ 1,529	$ 471	$ 128