Summary of Business Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended										12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Revenues:
Gross premiums written												$ 565,845		$ 590,233		$ 291,253
Net premiums written												470,940		501,244		273,181
Net premiums earned		$ 109,472		$ 119,553	$ 117,804	$ 121,636	$ 123,222		$ 124,707	$ 128,877	$ 127,337	468,465		504,143		268,519
Other income (loss)												10,345		3,400		555
Total revenues												478,810		507,543		269,074
Losses and Expenses:
Net losses and loss adjustment expenses		48,946		72,162	78,111	64,784	48,498		77,691	79,560	69,619	264,003		275,368		137,561
Acquisition costs and other underwriting expenses		47,889		48,129	48,542	52,090	51,185		50,934	50,926	48,258	196,650		201,303		109,619
Income (loss) from segments												18,157		30,872		21,894
Unallocated Items:
Net investment income		8,880		8,795	6,562	9,746	8,375		8,852	9,141	8,241	33,983		34,609		28,821
Net realized investment gains		30,778		1,928	(3,492)	(7,493)	3,842		(10,778)	6,532	(2,970)	21,721		(3,374)		35,860
Corporate and other operating expenses												(17,338)		(24,448)		(14,559)
Interest expense												(8,905)		(4,913)		(822)
Income before income taxes		46,535		10,598	(11,468)	1,953	29,463		(9,727)	9,772	3,238	47,618		32,746		71,194
Income tax expense (benefit)												2,250		8,723		(8,338)
Net income		38,373		$ 9,535	$ (5,165)	$ 7,125	27,304		$ (3,746)	$ 11,117	$ 6,794	49,868		41,469		62,856
Total assets		1,972,946					1,957,294					1,972,946		1,957,294		1,930,033
Personal Lines Segment
Revenues:
Gross premiums written	[2]											300,888	[1]	326,282	[3]
Net premiums written	[2]											226,228		254,035
Net premiums earned	[2]											236,170		253,048
Other income (loss)	[2]											3,097		2,872
Total revenues	[2]											239,267		255,920
Losses and Expenses:
Net losses and loss adjustment expenses	[2]											174,933		163,986
Acquisition costs and other underwriting expenses	[2]											103,289	[4]	99,140	[5]
Income (loss) from segments	[2]											(38,955)		(7,206)
Unallocated Items:
Total assets	[2]	456,654					510,503					456,654		510,503
Commercial Lines Segment
Revenues:
Gross premiums written	[2]											205,120		214,218		229,978
Net premiums written	[2]											184,911		197,526		212,965
Net premiums earned	[2]											190,727		199,304		211,165
Other income (loss)	[2]											7,472		621		620
Total revenues	[2]											198,199		199,925		211,785
Losses and Expenses:
Net losses and loss adjustment expenses	[2]											74,996		97,530		117,586
Acquisition costs and other underwriting expenses	[2]											77,297	[6]	83,170	[7]	88,983	[8]
Income (loss) from segments	[2]											45,906		19,225		5,216
Unallocated Items:
Total assets	[2]	804,418					729,097					804,418		729,097		1,288,763
Reinsurance Operations
Revenues:
Gross premiums written	[9]											59,837		49,733		61,275
Net premiums written	[9]											59,801		49,683		60,216
Net premiums earned	[9]											41,568		51,791		57,354
Other income (loss)	[9]											(224)		(93)		(65)
Total revenues	[9]											41,344		51,698		57,289
Losses and Expenses:
Net losses and loss adjustment expenses	[9]											14,074		13,852		19,975
Acquisition costs and other underwriting expenses	[9]											16,064		18,993		20,636
Income (loss) from segments	[9]											11,206		18,853		16,678
Unallocated Items:
Total assets	[9]	$ 711,874	[10]				$ 717,694	[10]				$ 711,874	[10]	$ 717,694	[10]	$ 641,270	[11]

[1] Includes $35,334 of business written by American Reliable that is ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

[2] Includes business ceded to the Company's Reinsurance Operations.

[3] Includes $55,829 of business written by American Reliable that is ceded to insurance companies owned by Assurant under a 100% quota share reinsurance agreement.

[4] Includes federal excise tax of $1,181 relating to cessions from Personal Lines to Reinsurance Operations.

[5] Includes federal excise tax of $1,265 relating to cessions from Personal Lines to Reinsurance Operations.

[6] Includes federal excise tax of $523 relating to cessions from Commercial Lines to Reinsurance Operations.

[7] Includes federal excise tax of $1,051 relating to cessions from Commercial Lines to Reinsurance Operations.

[8] Includes excise tax of $1,114 related to cessions from Commercial Lines to Reinsurance Operations.

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

[10] Comprised of Global Indemnity Reinsurance's total assets less its investment in subsidiaries

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