Summary of Business Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2018
Revenues:
Gross premiums written		$ 157,177		$ 135,606		$ 478,699		$ 418,670
Net premiums written		138,836		116,233		421,321		360,557
Net premiums earned		133,312		120,528		383,602		342,447
Other income (loss)		264		411		1,274		1,289
Total revenues		133,576		120,939		384,876		343,736
Losses and Expenses:
Net losses and loss adjustment expenses		73,583		80,493		201,979		195,426
Acquisition costs and other underwriting expenses		53,366		48,680		153,643		141,196
Income (loss) from segments		6,627		(8,234)		29,254		7,114
Unallocated Items:
Net investment income		11,348		11,750		32,393		34,108
Net realized investment gains (losses)		(2,690)		5,319		11,290		7,833
Corporate and other operating expenses		(3,858)		(3,475)		(11,702)		(23,653)
Interest expense		(5,023)		(4,924)		(15,088)		(14,725)
Income before income taxes		6,404		436		46,147		10,677
Income tax (expense) benefit		317		3,292		(5,163)		5,944
Net income		6,721		3,728		40,984		16,621
Total assets		2,084,156		1,958,046		2,084,156		1,958,046		$ 1,960,266
Commercial Specialty
Revenues:
Gross premiums written	[1]	73,175		63,177		214,467		186,923
Net premiums written	[1]	62,925		56,161		185,202		165,817
Net premiums earned	[1]	60,869		56,352		173,215		155,966
Other income (loss)	[1]			0		0		0
Total revenues	[1]	60,869		56,352		173,215		155,966
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	27,389		31,899		81,731		82,023
Acquisition costs and other underwriting expenses	[1]	24,820		22,533	[2]	70,522		62,789	[3]
Income (loss) from segments	[1]	8,660		1,920		20,962		11,154
Unallocated Items:
Net investment income	[1]	0		0		0		0
Net realized investment gains (losses)	[1]			0		0		0
Corporate and other operating expenses	[1]	0		0		0		0
Interest expense	[1]	0		0		0		0
Income before income taxes	[1]	0		0		0		0
Income tax (expense) benefit	[1]			0				0
Net income	[1]	0		0		0		0
Total assets	[1]	864,154		874,059		864,154		874,059
Specialty Property
Revenues:
Gross premiums written	[1]	42,611	[4]	43,912	[5]	128,771	[6]	132,286	[7]
Net premiums written	[1]	37,628		32,023		110,668		101,542
Net premiums earned	[1]	34,554		31,581		104,740		98,977
Other income (loss)	[1]	465		457		1,406		1,343
Total revenues	[1]	35,019		32,038		106,146		100,320
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	25,997		30,474		57,611		69,563
Acquisition costs and other underwriting expenses	[1]	14,571		12,781	[8]	44,163		42,548	[9]
Income (loss) from segments	[1]	(5,549)		(11,217)		4,372		(11,791)
Unallocated Items:
Net investment income	[1]	0		0		0		0
Net realized investment gains (losses)	[1]			0		0		0
Corporate and other operating expenses	[1]	0		0		0		0
Interest expense	[1]	0		0		0		0
Income before income taxes	[1]	0		0		0		0
Income tax (expense) benefit	[1]			0				0
Net income	[1]	0		0		0		0
Total assets	[1]	366,162		341,983		366,162		341,983
Farm, Ranch & Stable
Revenues:
Gross premiums written	[1]	21,410		19,160		65,872		59,496
Net premiums written	[1]	18,294		18,696		55,861		53,239
Net premiums earned	[1]	18,377		19,260		52,849		52,356
Other income (loss)	[1]	34		36		96		125
Total revenues	[1]	18,411		19,296		52,945		52,481
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	10,939		10,842		32,203		29,383
Acquisition costs and other underwriting expenses	[1]	7,776		8,259	[10]	22,403		22,898	[11]
Income (loss) from segments	[1]	(304)		195		(1,661)		200
Unallocated Items:
Net investment income	[1]	0		0		0		0
Net realized investment gains (losses)	[1]			0		0		0
Corporate and other operating expenses	[1]	0		0		0		0
Interest expense	[1]	0		0		0		0
Income before income taxes	[1]	0		0		0		0
Income tax (expense) benefit	[1]			0				0
Net income	[1]	0		0		0		0
Total assets	[1]	197,164		184,144		197,164		184,144
Reinsurance Operations
Revenues:
Gross premiums written	[6]	19,981		9,357		69,589		39,965
Net premiums written	[6]	19,989		9,353		69,590		39,959
Net premiums earned	[6]	19,512		13,335		52,798		35,148
Other income (loss)	[6]	(235)		(82)		(228)		(179)
Total revenues	[6]	19,277		13,253		52,570		34,969
Losses and Expenses:
Net losses and loss adjustment expenses	[6]	9,258		7,278		30,434		14,457
Acquisition costs and other underwriting expenses	[6]	6,199		5,107		16,555		12,961
Income (loss) from segments	[6]	3,820		868		5,581		7,551
Unallocated Items:
Net investment income	[6]	0		0		0		0
Net realized investment gains (losses)	[6]			0		0		0
Corporate and other operating expenses	[6]	0		0		0		0
Interest expense	[6]	0		0		0		0
Income before income taxes	[6]	0		0		0		0
Income tax (expense) benefit	[6]			0				0
Net income	[6]	0		0		0		0
Total assets	[6],[7]	$ 656,676		$ 557,860		$ 656,676		$ 557,860

[1] Includes business ceded to the Company’s Reinsurance Operations. This quota share agreement was cancelled effective January 1, 2018.

[2] Includes federal excise tax of $77 relating to cessions from Commercial Specialty to Reinsurance Operations.

[3] Includes federal excise tax of $367 relating to cessions from Commercial Specialty to Reinsurance Operations.

[4] Includes ($23) of business written by American Reliable that was ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

[5] Includes ($3) of business written by American Reliable that was ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

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

[7] Comprised of Global Indemnity Reinsurance’s total assets less its investment in subsidiaries.

[8] Includes federal excise tax of $64 relating to cessions from Specialty Property to Reinsurance Operations.

[9] Includes federal excise tax of $298 relating to cessions from Specialty Property to Reinsurance Operations.

[10] Includes federal excise tax of $28 relating to cessions from Farm, Ranch, & Stable to Reinsurance Operations.

[11] Includes federal excise tax of $137 relating to cessions from Farm, Ranch, & Stable to Reinsurance Operations.