Summary of Business Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018
Revenues:
Gross premiums written		$ 142,201		$ 124,247
Net premiums written		123,416		107,870
Net premiums earned		122,089		108,002
Other income		488		554
Total revenues		122,577		108,556
Losses and Expenses:
Net losses and loss adjustment expenses		58,321		56,072
Acquisition costs and other underwriting expenses		49,743		45,003
Income (loss) from segments		14,513		7,481
Unallocated Items:
Net investment income		7,219		11,404
Net realized investment gains (losses)		10,390		(316)
Corporate and other operating expenses		(3,205)		(9,260)
Interest expense		(5,023)		(4,861)
Income before income taxes		23,894		4,448
Income tax (expense) benefit		(4,294)		1,253
Net income		19,600		5,701
Total assets		1,984,908		1,963,714		$ 1,960,266
Commercial Specialty
Revenues:
Gross premiums written	[1]	64,213		53,773
Net premiums written	[1]	55,170		48,306
Net premiums earned	[1]	55,641		47,362
Other income	[1]	0		0
Total revenues	[1]	55,641		47,362
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	21,651		25,029
Acquisition costs and other underwriting expenses	[1]	22,812		19,205	[2]
Income (loss) from segments	[1]	11,178		3,128
Unallocated Items:
Net investment income	[1]	0		0
Net realized investment gains (losses)	[1]	0		0
Corporate and other operating expenses	[1]	0		0
Interest expense	[1]	0		0
Income before income taxes	[1]	0		0
Income tax (expense) benefit	[1]	0		0
Net income	[1]	0		0
Total assets	[1]	806,951		893,115
Specialty Property
Revenues:
Gross premiums written	[1]	39,674	[3]	41,344	[4]
Net premiums written	[1]	33,212		33,010
Net premiums earned	[1]	34,619		33,987
Other income	[1]	443		446
Total revenues	[1]	35,062		34,433
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	20,503		21,186
Acquisition costs and other underwriting expenses	[1]	14,653		14,954	[5]
Income (loss) from segments	[1]	(94)		(1,707)
Unallocated Items:
Net investment income	[1]	0		0
Net realized investment gains (losses)	[1]	0		0
Corporate and other operating expenses	[1]	0		0
Interest expense	[1]	0		0
Income before income taxes	[1]	0		0
Income tax (expense) benefit	[1]	0		0
Net income	[1]	0		0
Total assets	[1]	359,482		321,690
Farm, Ranch & Stable
Revenues:
Gross premiums written	[1]	20,765		18,821
Net premiums written	[1]	17,492		16,245
Net premiums earned	[1]	17,122		16,625
Other income	[1]	30		57
Total revenues	[1]	17,152		16,682
Losses and Expenses:
Net losses and loss adjustment expenses	[1]	8,138		6,435
Acquisition costs and other underwriting expenses	[1]	7,282		7,225	[6]
Income (loss) from segments	[1]	1,732		3,022
Unallocated Items:
Net investment income	[1]	0		0
Net realized investment gains (losses)	[1]	0		0
Corporate and other operating expenses	[1]	0		0
Interest expense	[1]	0		0
Income before income taxes	[1]	0		0
Income tax (expense) benefit	[1]	0		0
Net income	[1]	0		0
Total assets	[1]	193,567		173,218
Reinsurance Operations
Revenues:
Gross premiums written	[7]	17,549		10,309
Net premiums written	[7]	17,542		10,309
Net premiums earned	[7]	14,707		10,028
Other income	[7]	15		51
Total revenues	[7]	14,722		10,079
Losses and Expenses:
Net losses and loss adjustment expenses	[7]	8,029		3,422
Acquisition costs and other underwriting expenses	[7]	4,996		3,619
Income (loss) from segments	[7]	1,697		3,038
Unallocated Items:
Net investment income	[7]	0		0
Net realized investment gains (losses)	[7]	0		0
Corporate and other operating expenses	[7]	0		0
Interest expense	[7]	0		0
Income before income taxes	[7]	0		0
Income tax (expense) benefit	[7]	0		0
Net income	[7]	0		0
Total assets	[7],[8]	$ 624,908		$ 575,691

[1] Includes business ceded to the Company’s Reinsurance Operations.

[2] Includes federal excise tax of $174 relating to cessions from Commercial Specialty to Reinsurance Operations.

[3] Includes ($138) of business written by American Reliable that was ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

[4] Includes ($867) of business written by American Reliable that was ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

[5] Includes federal excise tax of $141 relating to cessions from Specialty Property to Reinsurance Operations.

[6] Includes federal excise tax of $65 relating to cessions from Farm, Ranch, & Stable to Reinsurance Operations.

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

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