Revision of Previously Issued Consolidated Financial Statements - Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Ceded premiums written	$ (78,140)			$ (83,408)		$ (231,891)	$ (239,267)
Net premiums written	90,964			113,056		269,947	342,430
Change in unearned premiums	3,383			3,664		22,836	19,587
Net premiums earned	94,347			116,720		292,783	362,017
Total revenue	97,350			120,293		313,591	349,761
Losses and loss adjustment expenses	63,706			122,555		209,674	308,278
Operating expenses	27,882			33,640		85,188	92,059
(Loss) income before tax	4,391			(37,792)		14,608	(102,484)
Income tax expense	946			(9,404)		3,037	(15,943)
Net income (loss)	$ 3,445			$ (28,388)		$ 11,571	$ (86,541)
Common stockholders net income per share:
Basic (in dollars per share)	$ 0.19			$ (1.56)		$ 0.64	$ (4.77)
Diluted (in dollars per share)	$ 0.19			$ (1.56)		$ 0.64	$ (4.77)
Incorrect Accounting For Reinsurance Treaties [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Ceded premiums written		$ (82,230)	$ (71,521)	$ (83,408)	$ (153,751)		$ (239,267)	$ (315,035)	$ (353,257)
Net premiums written		87,486	91,497	113,056	178,983		342,430	428,333	490,574
Change in unearned premiums		9,098	10,355	3,664	19,453		19,587	43,568	(56,282)
Net premiums earned		96,584	101,852	116,720	198,436		362,017	471,901	434,292
Total revenue		104,188	112,053	120,293	216,241		349,761	468,848	483,786
Losses and loss adjustment expenses		76,489	69,479	122,555	145,968		308,278	406,907	360,546
Operating expenses		27,334	29,973	33,640	57,307		92,059	123,919	117,032
(Loss) income before tax		(1,010)	11,227	(37,792)	10,217		(102,484)	(115,768)	(1,674)
Income tax expense		(165)	2,256	(9,404)	2,091		(15,943)	(21,417)	(542)
Net income (loss)		$ (845)	$ 8,971	$ (28,388)	$ 8,126		$ (86,541)	$ (94,351)	$ (1,132)
Common stockholders net income per share:
Basic (in dollars per share)		$ (0.05)	$ 0.49	$ (1.56)	$ 0.45		$ (4.77)	$ (5.20)	$ (0.06)
Diluted (in dollars per share)		$ (0.05)	$ 0.49	$ (1.56)	$ 0.45		$ (4.77)	$ (5.20)	$ (0.06)
Incorrect Accounting For Reinsurance Treaties [Member] | As Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Ceded premiums written		$ (80,582)	$ (69,871)	$ (80,353)	$ (150,453)		$ (230,094)	$ (304,395)	$ (347,279)
Net premiums written		89,134	93,147	116,111	182,281		351,603	438,973	496,552
Change in unearned premiums		9,477	11,071	3,449	20,548		17,486	42,825	(59,675)
Net premiums earned		98,611	104,218	119,560	202,829		369,089	481,798	436,877
Total revenue		106,215	114,419	123,133	220,634		356,833	478,745	486,371
Losses and loss adjustment expenses		77,719	70,903	124,253	148,622		312,531	412,851	362,165
Operating expenses		27,653	30,441	34,296	58,094		93,703	126,266	117,357
(Loss) income before tax		(532)	11,700	(37,306)	11,168		(101,309)	(114,162)	(1,032)
Income tax expense		(65)	2,355	(9,302)	2,290		(15,696)	(22,507)	(407)
Net income (loss)		$ (467)	$ 9,345	$ (28,004)	$ 8,878		$ (85,613)	$ (91,655)	$ (625)
Common stockholders net income per share:
Basic (in dollars per share)		$ (0.03)	$ 0.52	$ (1.54)	$ 0.49		$ (4.72)	$ (5.05)	$ (0.03)
Diluted (in dollars per share)		$ (0.03)	$ 0.52	$ (1.54)	$ 0.49		$ (4.72)	$ (5.05)	$ (0.03)
Incorrect Accounting For Reinsurance Treaties [Member] | Revisions [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Ceded premiums written		$ (1,648)	$ (1,650)	$ (3,055)	$ (3,298)		$ (9,173)	$ (10,640)	$ (5,978)
Net premiums written		(1,648)	(1,650)	(3,055)	(3,298)		(9,173)	(10,640)	(5,978)
Change in unearned premiums		(379)	(716)	215	(1,095)		2,101	743	3,393
Net premiums earned		(2,027)	(2,366)	(2,840)	(4,393)		(7,072)	(9,897)	(2,585)
Total revenue		(2,027)	(2,366)	(2,840)	(4,393)		(7,072)	(9,897)	(2,585)
Losses and loss adjustment expenses		(1,230)	(1,424)	(1,698)	(2,654)		(4,253)	(5,944)	(1,619)
Operating expenses		(319)	(468)	(656)	(787)		(1,644)	(2,347)	(325)
(Loss) income before tax		(478)	(473)	(486)	(951)		(1,175)	(1,606)	(642)
Income tax expense		(100)	(99)	(102)	(199)		(247)	1,090	(135)
Net income (loss)		$ (378)	$ (374)	$ (384)	$ (752)		$ (928)	$ (2,696)	$ (507)
Common stockholders net income per share:
Basic (in dollars per share)		$ (0.02)	$ (0.03)	$ (0.02)	$ (0.04)		$ (0.05)	$ (0.15)	$ (0.03)
Diluted (in dollars per share)		$ (0.02)	$ (0.03)	$ (0.02)	$ (0.04)		$ (0.05)	$ (0.15)	$ (0.03)