Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Results of Operations (Unaudited) [Abstract]
Net premiums earned	$ 97,075	$ 89,100	$ 67,996	$ 73,974	$ 69,141	$ 71,235	$ 68,726	$ 66,909	$ 328,145	$ 276,011	$ 263,335
Net investment income	5,661	4,027	4,716	3,692	3,982	3,513	3,549	3,440	18,095	14,483	12,498
Net realized gains (losses) on investments	4,152	5,944	3,296	6,294	6,204	7,732	280	9,012	19,686	23,228	(1,261)
Losses and loss expenses incurred	66,492	60,673	71,754	48,599	48,366	56,827	42,666	38,623	247,518	186,481	155,750
Net income (loss)	$ 16,476	$ 7,434	$ (12,343)	$ 6,756	$ 4,864	$ 4,001	$ 5,969	$ 14,112	$ 18,323	$ 28,945	$ 23,283
Net income (loss) per share - diluted (in dollars per share)	$ 1.10	$ 0.49	$ (0.82)	$ 0.45	$ 0.32	$ 0.27	$ 0.40	$ 0.94