Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Segment	Jun. 30, 2017 USD ($)
Segment Information [Abstract]
Number of reportable segments | Segment			1
Summary of Segment Revenue [Abstract]
Net premiums earned	$ 111,940	$ 67,996	$ 217,402	$ 141,971
Net investment income	5,796	4,716	10,432	8,408
Net realized and unrealized gains (losses) on investments	(3,435)	3,296	(7,968)	9,590
Commissions and other income	2,263	1,400	4,076	2,380
Total revenues	116,564	77,408	223,942	162,349
Property and Casualty Insurance [Member]
Summary of Segment Revenue [Abstract]
Net premiums earned	111,940	67,996	217,402	141,971
Net investment income	5,796	4,716	10,432	8,408
Net realized and unrealized gains (losses) on investments	(3,435)	3,296	(7,968)	9,590
Commissions and other income	2,263	1,400	4,076	2,380
Total revenues	$ 116,564	$ 77,408	$ 223,942	$ 162,349