Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Dec. 31, 2015		Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
ASSETS:
Cash and cash equivalents		$ 674,627		$ 441,850		$ 729,023		$ 495,112
Reinsurance recoverables and trade receivables, net		181,326		189,869
Inventories, net		75,032		69,472
Prepaid expenses		180,628		126,296
Investments, fixed maturities and marketable equities		1,463,997		1,304,962
Investments, other		323,039		268,720
Deferred policy acquisition costs, net		129,218		115,422
Other assets		90,989		106,157
Related party assets		92,677		141,790
Subtotal assets		$ 3,211,533		$ 2,764,538
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		$ 589,492		$ 467,482
Buildings and improvements		2,026,840		1,728,033
Furniture and equipment		383,914		355,349
Property, plant and equipment, gross		6,625,450		6,047,493
Less: Accumulated depreciation		(2,074,449)		(1,939,856)
Total property, plant and equipment		4,551,001		4,107,637
Total assets		7,762,534		6,872,175		6,906,532
Liabilities:
Accounts payable and accrued expenses		446,044		496,370
Notes, loans and leases payable		2,424,671		2,190,869
Policy benefits and losses, claims and loss expenses payable		1,073,600		1,062,188
Liabilities from investment contracts		891,243		685,745
Other policyholders' funds and liabilities		8,439		7,764
Deferred income		18,977		18,081
Deferred income taxes, net		$ 674,621		526,799
Related party liabilities
Total liabilities		$ 5,537,595		4,987,816
Stockholders' equity:
Additional paid-in capital		451,492		449,668
Accumulated other comprehensive loss		(59,068)		(34,365)
Retained earnings		2,500,659		2,142,600
Unearned employee stock ownership plan shares		(991)		(6,391)
Total stockholders' equity		2,224,939		1,884,359
Total liabilities and stockholders' equity		7,762,534		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		463,034		436,642
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		$ 3,162,170		$ 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		649,191		431,873		713,702		464,710
Reinsurance recoverables and trade receivables, net		37,598		32,364
Inventories, net		75,032		69,472
Prepaid expenses		$ 180,628		$ 126,296
Investments, fixed maturities and marketable equities
Investments, other		$ 31,107		$ 27,637
Deferred policy acquisition costs, net
Other assets		$ 87,890		$ 101,689
Related party assets		94,370		144,040
Subtotal assets		1,155,816		933,371
Investments in subsidiaries		455,716		443,462
Property, plant and equipment, at cost:
Land		589,492		467,482
Buildings and improvements		2,026,840		1,728,033
Furniture and equipment		383,914		355,349
Property, plant and equipment, gross		6,625,450		6,047,493
Less: Accumulated depreciation		(2,074,449)		(1,939,856)
Total property, plant and equipment		4,551,001		4,107,637
Total assets		6,162,533		5,484,470
Liabilities:
Accounts payable and accrued expenses		425,022		489,140
Notes, loans and leases payable		2,424,671		2,190,869
Policy benefits and losses, claims and loss expenses payable		$ 382,701		$ 363,552
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		$ 18,977		$ 18,081
Deferred income taxes, net		673,058		524,550
Related party liabilities		13,165		13,919
Total liabilities		3,937,594		3,600,111
Stockholders' equity:
Additional paid-in capital		451,702		449,878
Accumulated other comprehensive loss		(59,068)		(34,365)
Retained earnings		2,500,449		2,142,390
Unearned employee stock ownership plan shares		(991)		(6,391)
Total stockholders' equity		2,224,939		1,884,359
Total liabilities and stockholders' equity		6,162,533		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		463,034		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		$ 3,162,170		$ 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		13,882	[1]	8,495	[2]	10,259	[3]	12,758	[3]
Reinsurance recoverables and trade receivables, net		$ 113,429	[1]	$ 125,506	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		$ 236,058	[1]	$ 228,530	[2]
Investments, other		$ 47,521	[1]	$ 50,867	[2]
Deferred policy acquisition costs, net			[1]		[2]
Other assets		$ 651	[1]	$ 1,924	[2]
Related party assets		13,118	[1]	13,268	[2]
Subtotal assets		$ 424,659	[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		$ 424,659	[1]	$ 428,590	[2]
Liabilities:
Accounts payable and accrued expenses		$ 821	[1]	$ 1,235	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		$ 256,342	[1]	$ 271,744	[2]
Liabilities from investment contracts			[1]		[2]
Other policyholders' funds and liabilities		$ 2,833	[1]	$ 2,837	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		$ (15,243)	[1]	$ (18,592)	[2]
Related party liabilities		2,046	[1]	2,073	[2]
Total liabilities		246,799	[1]	259,297	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]	91,120	[2]
Accumulated other comprehensive loss		5,209	[1]	8,871	[2]
Retained earnings		$ 78,230	[1]	$ 66,001	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		$ 177,860	[1]	$ 169,293	[2]
Total liabilities and stockholders' equity		$ 424,659	[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		$ 11,554	[1]	$ 1,482	[2]	$ 5,062	[3]	$ 17,644	[3]
Reinsurance recoverables and trade receivables, net		$ 30,299	[1]	$ 31,999	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		$ 1,227,939	[1]	$ 1,076,432	[2]
Investments, other		244,411	[1]	190,216	[2]
Deferred policy acquisition costs, net		129,218	[1]	115,422	[2]
Other assets		2,448	[1]	2,544	[2]
Related party assets		555	[1]	586	[2]
Subtotal assets		$ 1,646,424	[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		$ 1,646,424	[1]	$ 1,418,681	[2]
Liabilities:
Accounts payable and accrued expenses		$ 20,201	[1]	$ 5,995	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		$ 434,557	[1]	$ 426,892	[2]
Liabilities from investment contracts		891,243	[1]	685,745	[2]
Other policyholders' funds and liabilities		$ 5,606	[1]	$ 4,927	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		$ 16,806	[1]	$ 20,841	[2]
Related party liabilities		155	[1]	112	[2]
Total liabilities		1,368,568	[1]	1,144,512	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]	26,271	[2]
Accumulated other comprehensive loss		23,007	[1]	32,310	[2]
Retained earnings		$ 226,078	[1]	$ 213,088	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		$ 277,856	[1]	$ 274,169	[2]
Total liabilities and stockholders' equity		$ 1,646,424	[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]
Consolidation, 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]	$ (455,716)		$ (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		$ (471,082)		$ (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, net
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]	(28,216)		(41,181)
Retained earnings	[5]	$ (304,098)		$ (278,879)
Unearned employee stock ownership plan shares
Total stockholders' equity		$ (455,716)		$ (443,462)
Total liabilities and stockholders' equity		$ (471,082)		$ (459,566)
Consolidation, Eliminations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Consolidation, Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Consolidation, Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Consolidation, Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Consolidation, Eliminations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Consolidation, Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	[5]	$ (5,801)		$ (5,801)
Consolidation, Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value
Consolidation, Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value

[1] Balances as of September 30, 2015

[2] Balances as of December 31, 2014

[3] Balance for the period ended September 30, 2014

[4] Eliminate intercompany receivables and payables

[5] Eliminate investment in subsidiaries