Summary of Business Segment Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Revenues:
Gross written premiums		$ 682,122		$ 606,603		$ 636,861
Net written premiums		580,068		548,167		562,089
Net earned premiums		595,610		567,699		525,262
Other income (loss)		1,815		2,038		1,816
Total revenues		597,425		569,737		527,078
Losses and Expenses:
Net losses and loss adjustment expenses		384,964		336,201		275,402
Acquisition costs and other underwriting expenses		222,841		215,607		208,403
Income (loss) from segments		(10,380)		17,929		43,273
Unallocated Items:
Net investment income		37,020		28,392		42,052
Net realized investment gains (losses)		15,887		(14,662)		35,342
Other income		27,936		80
Corporate and other operating expenses		(27,179)		(41,998)		(18,888)
Interest expense		(10,481)		(15,792)		(20,022)
Income (loss) before income taxes		32,803		(29,111)		81,757
Income tax expense (benefit)		(3,449)		8,105		(11,742)
Net income (loss)		29,354		(21,006)		70,015
Loss on extinguishment of debt		0		(3,060)		0
Total assets		2,012,809		1,904,908		2,075,885
Segment Assets
Unallocated Items:
Total assets		1,627,729		1,518,879		1,401,740
Corporate Assets
Unallocated Items:
Total assets		385,080		386,029		674,145
Commercial Specialty
Revenues:
Gross written premiums		380,879		323,986		299,107
Net written premiums		355,428		300,348		273,891
Net earned premiums		340,029		292,331		248,073
Other income (loss)		1,028		888		827
Total revenues		341,057		293,219		248,900
Losses and Expenses:
Net losses and loss adjustment expenses		212,936		151,369		105,830
Acquisition costs and other underwriting expenses		123,436		107,677		101,249
Income (loss) from segments		4,685		34,173		41,821
Unallocated Items:
Net investment income				0
Net realized investment gains (losses)		0		0		0
Other income				0
Corporate and other operating expenses				0
Interest expense				0
Income (loss) before income taxes		0		0		0
Income tax expense (benefit)		0		0		0
Net income (loss)		0		0		0
Loss on extinguishment of debt				0
Total assets				0		0
Commercial Specialty | Segment Assets
Unallocated Items:
Total assets		933,961		847,902		705,518
Commercial Specialty | Corporate Assets
Unallocated Items:
Total assets				0		0
Farm, Ranch & Stable
Revenues:
Gross written premiums		81,728		85,646		87,745
Net written premiums		70,472		74,163		74,416
Net earned premiums		71,899		76,166		71,312
Other income (loss)		155		142		132
Total revenues		72,054		76,308		71,444
Losses and Expenses:
Net losses and loss adjustment expenses		43,369		47,151		42,700
Acquisition costs and other underwriting expenses		28,700		29,761		29,551
Income (loss) from segments		(15)		(604)		(807)
Unallocated Items:
Net investment income				0
Net realized investment gains (losses)		0		0		0
Other income		0		0
Corporate and other operating expenses				0
Interest expense				0
Income (loss) before income taxes		0		0		0
Income tax expense (benefit)		0		0		0
Net income (loss)		0		0		0
Loss on extinguishment of debt				0
Total assets				0		0
Farm, Ranch & Stable | Segment Assets
Unallocated Items:
Total assets		142,213		152,037		136,891
Farm, Ranch & Stable | Corporate Assets
Unallocated Items:
Total assets				0		0
Reinsurance Operations
Revenues:
Gross written premiums		106,540	[1]	55,616	[2]	34,837	[1]
Net written premiums		106,540	[1]	55,616	[2]	34,837	[1]
Net earned premiums		77,802	[1]	46,105	[2]	19,154	[1]
Other income (loss)		(95)	[1]	191	[2]	(136)	[1]
Total revenues		77,707	[1]	46,296	[2]	19,018	[1]
Losses and Expenses:
Net losses and loss adjustment expenses		48,709	[1]	28,718	[2]	10,872	[1]
Acquisition costs and other underwriting expenses		27,086	[1]	16,148	[2]	5,085	[1]
Income (loss) from segments		1,912	[1]	1,430	[2]	3,061	[1]
Unallocated Items:
Net investment income	[2]			0
Net realized investment gains (losses)		0	[1]	0	[2]	0	[1]
Other income		0	[1]	0	[2]
Corporate and other operating expenses	[2]			0
Interest expense	[2]			0
Income (loss) before income taxes		0	[1]	0	[2]	0	[1]
Income tax expense (benefit)		0	[1]	0	[2]	0	[1]
Net income (loss)		0	[1]	0	[2]	0	[1]
Loss on extinguishment of debt	[2]			0
Total assets				0	[2]	0	[1]
Reinsurance Operations | Segment Assets
Unallocated Items:
Total assets		247,366	[1]	137,950	[2]	85,398	[1]
Reinsurance Operations | Corporate Assets
Unallocated Items:
Total assets				0	[2]	0	[1]
Exited Lines Segment
Revenues:
Gross written premiums		112,975		141,355		215,172
Net written premiums		47,628		118,040		178,945
Net earned premiums		105,880		153,097		186,723
Other income (loss)		727		817		993
Total revenues		106,607		153,914		187,716
Losses and Expenses:
Net losses and loss adjustment expenses		79,950		108,963		116,000
Acquisition costs and other underwriting expenses		43,619		62,021		72,518
Income (loss) from segments		(16,962)		(17,070)		(802)
Unallocated Items:
Net investment income		0		0		0
Net realized investment gains (losses)		0		0		0
Other income		0		0
Corporate and other operating expenses		0		0		0
Interest expense		0		0		0
Income (loss) before income taxes		0		0		0
Income tax expense (benefit)		0		0		0
Net income (loss)		0		0		0
Loss on extinguishment of debt				0
Total assets		0		0		0
Exited Lines Segment | Segment Assets
Unallocated Items:
Total assets		304,189		380,990		473,933
Exited Lines Segment | Corporate Assets
Unallocated Items:
Total assets		$ 0		$ 0		$ 0

[1] External business only, excluding business assumed from affiliates. 

[2] External business only, excluding business assumed from affiliates.