Investments, Major Categories of Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment Income, Net [Abstract]
Investment Income	$ 28,916	$ 25,001	$ 20,422
Investment expenses	(2,667)	(2,953)	(2,327)
Net investment income	26,249	22,048	18,095
Interest on Fixed Income Securities [Member]
Investment Income, Net [Abstract]
Investment Income	24,620	19,092	15,340
Dividends on Equity Securities [Member]
Investment Income, Net [Abstract]
Investment Income	2,320	4,380	4,611
Money Market Funds, Short term and Other [Member]
Investment Income, Net [Abstract]
Investment Income	$ 1,976	$ 1,529	$ 471