Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Mar. 31, 2016		Dec. 31, 2015	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014		Mar. 31, 2013
ASSETS:
Cash and cash equivalents		$ 600,646			$ 441,850			$ 495,112		$ 463,744
Reinsurance recoverables and trade receivables, net		175,210			189,869
Inventories, net		79,756			69,472
Prepaid expenses		134,300			126,296
Investments, fixed maturities and marketable equities		1,510,538			1,304,962
Investments, other		310,072			268,720
Deferred policy acquisition costs, net		136,386			115,422
Other assets		100,572			106,157
Related party assets		85,734			141,790
Subtotal assets		$ 3,133,214			$ 2,764,538
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		$ 587,347			$ 467,482
Buildings and improvements		2,187,400			1,728,033
Furniture and equipment		399,943			355,349
Property, plant and equipment (gross)		7,151,244			6,047,493
Less: Accumulated depreciation		(2,133,733)			(1,939,856)
Total property, plant and equipment		5,017,511			4,107,637
Total assets		8,150,725			6,872,175			5,998,978
Liabilities:
Accounts payable and accrued expenses		502,613			496,370
Notes, loans and leases payable		2,688,758			2,190,869
Policy benefits and losses, claims and loss expenses payable		1,071,412			1,062,188
Liabilities from investment contracts		951,490			685,745
Other policyholders' funds and liabilities		8,650			7,764
Deferred income		22,784			18,081
Deferred income taxes		$ 653,612			$ 526,799
Related party liabilities
Total liabilities		$ 5,899,319			$ 4,987,816
Stockholders' equity:
Additional paid-in capital		451,629			449,668
Accumulated other comprehensive loss		(60,525)			(34,365)
Retained earnings		2,533,641			2,142,600
Unearned employee stock ownership plan shares		(6,186)			(6,391)
Total stockholders' equity		2,251,406			1,884,359
Total liabilities and stockholders' equity		8,150,725			6,872,175
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		462,379			436,642
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		$ 3,514,175			$ 3,059,987
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		$ 10,497			$ 10,497
Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(525,653)			(525,653)
Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(151,997)			(151,997)
Operating Segments [Member] | Moving and Storage Consolidations [Member]
ASSETS:
Cash and cash equivalents		585,666			431,873			464,710		427,560
Reinsurance recoverables and trade receivables, net		34,451			32,364
Inventories, net		79,756			69,472
Prepaid expenses		$ 134,300			$ 126,296
Investments, fixed maturities and marketable equities
Investments, other		$ 21,431			$ 27,637
Deferred policy acquisition costs, net
Other assets		$ 95,081			$ 101,689
Related party assets		88,022			144,040
Subtotal assets		1,038,707			933,371
Investments in subsidiaries		432,277			443,462
Property, plant and equipment, at cost:
Land		587,347			467,482
Buildings and improvements		2,187,400			1,728,033
Furniture and equipment		399,943			355,349
Property, plant and equipment (gross)		7,151,244			6,047,493
Less: Accumulated depreciation		(2,133,733)			(1,939,856)
Total property, plant and equipment		5,017,511			4,107,637
Total assets		6,488,495			5,484,470
Liabilities:
Accounts payable and accrued expenses		492,982			489,140
Notes, loans and leases payable		2,688,758			2,190,869
Policy benefits and losses, claims and loss expenses payable		$ 386,366			$ 363,552
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		$ 22,784			$ 18,081
Deferred income taxes		633,061			524,550
Related party liabilities		13,138			13,919
Total liabilities		4,237,089			3,600,111
Stockholders' equity:
Additional paid-in capital		451,839			449,878
Accumulated other comprehensive loss		(60,525)			(34,365)
Retained earnings		2,533,431			2,142,390
Unearned employee stock ownership plan shares		(6,186)			(6,391)
Total stockholders' equity		2,251,406			1,884,359
Total liabilities and stockholders' equity		6,488,495			5,484,470
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		462,379			436,642
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		$ 3,514,175			$ 3,059,987
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		$ 10,497			$ 10,497
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(525,653)			(525,653)
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(151,997)			(151,997)
Operating Segments [Member] | Property and Casualty Insurance [Member]
ASSETS:
Cash and cash equivalents		14,049	[1]		8,495	[2]		12,758	[3]	14,120	[3]
Reinsurance recoverables and trade receivables, net		$ 111,978	[1]		$ 125,506	[2]
Inventories, net			[1]			[2]
Prepaid expenses			[1]			[2]
Investments, fixed maturities and marketable equities		$ 238,570	[1]		$ 228,530	[2]
Investments, other		$ 47,374	[1]		$ 50,867	[2]
Deferred policy acquisition costs, net			[1]			[2]
Other assets		$ 3,088	[1]		$ 1,924	[2]
Related party assets		12,465	[1]		13,268	[2]
Subtotal assets		$ 427,524	[1]		$ 428,590	[2]
Investments in subsidiaries			[1]			[2]
Property, plant and equipment, at cost:
Land			[1]			[2]
Buildings and improvements			[1]			[2]
Furniture and equipment			[1]			[2]
Property, plant and equipment (gross)			[1]			[2]
Less: Accumulated depreciation			[1]			[2]
Total property, plant and equipment			[1]			[2]
Total assets		$ 427,524	[1]		$ 428,590	[2]
Liabilities:
Accounts payable and accrued expenses		$ 1,535	[1]		$ 1,235	[2]
Notes, loans and leases payable			[1]			[2]
Policy benefits and losses, claims and loss expenses payable		$ 252,819	[1]	$ 271,744	$ 271,744	[2]	$ 295,216
Liabilities from investment contracts			[1]			[2]
Other policyholders' funds and liabilities		$ 3,017	[1]		$ 2,837	[2]
Deferred income			[1]			[2]
Deferred income taxes		$ 7,526	[1]		$ (18,592)	[2]
Related party liabilities		2,067	[1]		2,073	[2]
Total liabilities		266,964	[1]		259,297	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]		91,120	[2]
Accumulated other comprehensive loss		3,611	[1]		8,871	[2]
Retained earnings		$ 62,528	[1]		$ 66,001	[2]
Unearned employee stock ownership plan shares			[1]			[2]
Total stockholders' equity		$ 160,560	[1]		$ 169,293	[2]
Total liabilities and stockholders' equity		$ 427,524	[1]		$ 428,590	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		$ 3,301	[1]		$ 3,301	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Life Insurance [Member]
ASSETS:
Cash and cash equivalents		$ 931	[1]		$ 1,482	[2]		$ 17,644	[3]	$ 22,064	[3]
Reinsurance recoverables and trade receivables, net		$ 28,781	[1]		$ 31,999	[2]
Inventories, net			[1]			[2]
Prepaid expenses			[1]			[2]
Investments, fixed maturities and marketable equities		$ 1,271,968	[1]		$ 1,076,432	[2]
Investments, other		241,267	[1]		190,216	[2]
Deferred policy acquisition costs, net		136,386	[1]		115,422	[2]
Other assets		2,403	[1]		2,544	[2]
Related party assets		613	[1]		586	[2]
Subtotal assets		$ 1,682,349	[1]		$ 1,418,681	[2]
Investments in subsidiaries			[1]			[2]
Property, plant and equipment, at cost:
Land			[1]			[2]
Buildings and improvements			[1]			[2]
Furniture and equipment			[1]			[2]
Property, plant and equipment (gross)			[1]			[2]
Less: Accumulated depreciation			[1]			[2]
Total property, plant and equipment			[1]			[2]
Total assets		$ 1,682,349	[1]		$ 1,418,681	[2]
Liabilities:
Accounts payable and accrued expenses		$ 8,096	[1]		$ 5,995	[2]
Notes, loans and leases payable			[1]			[2]
Policy benefits and losses, claims and loss expenses payable		$ 432,227	[1]		$ 426,892	[2]
Liabilities from investment contracts		951,490	[1]		685,745	[2]
Other policyholders' funds and liabilities		$ 5,633	[1]		$ 4,927	[2]
Deferred income			[1]			[2]
Deferred income taxes		$ 13,025	[1]		$ 20,841	[2]
Related party liabilities		161	[1]		112	[2]
Total liabilities		1,410,632	[1]		1,144,512	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]		26,271	[2]
Accumulated other comprehensive loss		10,504	[1]		32,310	[2]
Retained earnings		$ 232,442	[1]		$ 213,088	[2]
Unearned employee stock ownership plan shares			[1]			[2]
Total stockholders' equity		$ 271,717	[1]		$ 274,169	[2]
Total liabilities and stockholders' equity		$ 1,682,349	[1]		$ 1,418,681	[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		$ 2,500	[1]		$ 2,500	[2]
Operating Segments [Member] | Life Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Eliminations [Member]
ASSETS:
Cash and cash equivalents
Reinsurance recoverables and trade receivables, net
Inventories, net
Prepaid expenses
Investments, fixed maturities and marketable equities
Investments, other
Deferred policy acquisition costs, net
Other assets
Related party assets	[4]	$ (15,366)			$ (16,104)
Subtotal assets		(15,366)			(16,104)
Investments in subsidiaries	[5]	$ (432,277)			$ (443,462)
Property, plant and equipment, at cost:
Land
Buildings and improvements
Furniture and equipment
Property, plant and equipment (gross)
Less: Accumulated depreciation
Total property, plant and equipment
Total assets		$ (447,643)			$ (459,566)
Liabilities:
Accounts payable and accrued expenses
Notes, loans and leases payable
Policy benefits and losses, claims and loss expenses payable
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income
Deferred income taxes
Related party liabilities	[4]	$ (15,366)			$ (16,104)
Total liabilities		(15,366)			(16,104)
Stockholders' equity:
Additional paid-in capital	[5]	(117,601)			(117,601)
Accumulated other comprehensive loss	[5]	(14,115)			(41,181)
Retained earnings	[5]	$ (294,760)			$ (278,879)
Unearned employee stock ownership plan shares
Total stockholders' equity		$ (432,277)			$ (443,462)
Total liabilities and stockholders' equity		$ (447,643)			$ (459,566)
Eliminations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	[5]	$ (5,801)			$ (5,801)
Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value
Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value

[1] Balances as of December 31, 2015

[2] Balances as of December 31, 2014

[3] Balance for the period ended December 31, 2013

[4] Eliminate intercompany receivables and payables

[5] Eliminate investment in subsidiaries