Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Sep. 30, 2016		Mar. 31, 2016		Sep. 30, 2015		Mar. 31, 2015
ASSETS:
Cash and cash equivalents		$ 921,327		$ 600,646		$ 961,647		$ 441,850
Reinsurance recoverables and trade receivables, net		183,243		175,210
Inventories, net		81,609		79,756
Prepaid expenses		87,968		134,300
Investments, fixed maturities and marketable equities		1,632,420		1,510,538
Investments, other		382,065		310,072
Deferred policy acquisition costs, net		118,652		136,386
Other assets		85,600		77,210
Related party assets		80,171		85,734
Subtotal assets		3,573,055		3,109,852
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		616,969		587,347
Buildings and improvements		2,401,802		2,187,400
Furniture and equipment		448,990		399,943
Property, plant and equipment, gross		7,678,480		7,151,244
Less: Accumulated depreciation		(2,244,417)		(2,133,733)
Total property, plant and equipment		5,434,063		5,017,511
Total assets		9,007,118		8,127,363		7,600,545
Liabilities:
Accounts payable and accrued expenses		438,921		502,613
Notes, loans and leases payable		2,992,490		2,665,396
Policy benefits and losses, claims and loss expenses payable		1,088,128		1,071,412
Liabilities from investment contracts		1,043,129		951,490
Other policyholders' funds and liabilities		10,211		8,650
Deferred income		27,801		22,784
Deferred income taxes, net		791,524		653,612
Related party liabilities
Total liabilities		6,392,204		5,875,957
Stockholders' equity:
Additional paid-in capital		451,909		451,629
Accumulated other comprehensive loss		(19,890)		(60,525)
Retained earnings		2,857,289		2,533,641
Unearned employee stock ownership plan shares		(7,241)		(6,186)
Total stockholders' equity		2,614,914		2,251,406
Total liabilities and stockholders' equity		9,007,118		8,127,363
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		490,451		462,379
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		3,720,268		3,514,175
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		907,861		585,666		941,398		431,873
Reinsurance recoverables and trade receivables, net		40,590		34,451
Inventories, net		81,609		79,756
Prepaid expenses		87,968		134,300
Investments, fixed maturities and marketable equities
Investments, other		22,579		21,431
Deferred policy acquisition costs, net
Other assets		82,272		71,719
Related party assets		82,278		88,022
Subtotal assets		1,305,157		1,015,345
Investments in subsidiaries		488,557		432,277
Property, plant and equipment, at cost:
Land		616,969		587,347
Buildings and improvements		2,401,802		2,187,400
Furniture and equipment		448,990		399,943
Property, plant and equipment, gross		7,678,480		7,151,244
Less: Accumulated depreciation		(2,244,417)		(2,133,733)
Total property, plant and equipment		5,434,063		5,017,511
Total assets		7,227,777		6,465,133
Liabilities:
Accounts payable and accrued expenses		431,130		492,982
Notes, loans and leases payable		2,992,490		2,665,396
Policy benefits and losses, claims and loss expenses payable		399,325		386,366
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		27,801		22,784
Deferred income taxes, net		749,144		633,061
Related party liabilities		12,973		13,138
Total liabilities		4,612,863		4,213,727
Stockholders' equity:
Additional paid-in capital		452,119		451,839
Accumulated other comprehensive loss		(19,890)		(60,525)
Retained earnings		2,857,079		2,533,431
Unearned employee stock ownership plan shares		(7,241)		(6,186)
Total stockholders' equity		2,614,914		2,251,406
Total liabilities and stockholders' equity		7,227,777		6,465,133
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		490,451		462,379
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		3,720,268		3,514,175
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		11,775	[1]	14,049	[2]	13,166	[3]	8,495	[3]
Reinsurance recoverables and trade receivables, net		111,548	[1]	111,978	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		245,627	[1]	238,570	[2]
Investments, other		66,862	[1]	47,374	[2]
Deferred policy acquisition costs, net			[1]		[2]
Other assets		1,005	[1]	3,088	[2]
Related party assets		13,246	[1]	12,465	[2]
Subtotal assets		450,063	[1]	427,524	[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		450,063	[1]	427,524	[2]
Liabilities:
Accounts payable and accrued expenses		3,303	[1]	1,535	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		249,931	[1]	252,819	[2]
Liabilities from investment contracts			[1]		[2]
Other policyholders' funds and liabilities		3,581	[1]	3,017	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		12,028	[1]	7,526	[2]
Related party liabilities		2,780	[1]	2,067	[2]
Total liabilities		271,623	[1]	266,964	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]	91,120	[2]
Accumulated other comprehensive loss		11,926	[1]	3,611	[2]
Retained earnings		72,093	[1]	62,528	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		178,440	[1]	160,560	[2]
Total liabilities and stockholders' equity		450,063	[1]	427,524	[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		1,691	[1]	931	[2]	7,083	[3]	1,482	[3]
Reinsurance recoverables and trade receivables, net		31,105	[1]	28,781	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		1,386,793	[1]	1,271,968	[2]
Investments, other		292,624	[1]	241,267	[2]
Deferred policy acquisition costs, net		118,652	[1]	136,386	[2]
Other assets		2,323	[1]	2,403	[2]
Related party assets		507	[1]	613	[2]
Subtotal assets		1,833,695	[1]	1,682,349	[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		1,833,695	[1]	1,682,349	[2]
Liabilities:
Accounts payable and accrued expenses		4,488	[1]	8,096	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		438,872	[1]	432,227	[2]
Liabilities from investment contracts		1,043,129	[1]	951,490	[2]
Other policyholders' funds and liabilities		6,630	[1]	5,633	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		30,352	[1]	13,025	[2]
Related party liabilities		107	[1]	161	[2]
Total liabilities		1,523,578	[1]	1,410,632	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]	26,271	[2]
Accumulated other comprehensive loss		41,590	[1]	10,504	[2]
Retained earnings		239,756	[1]	232,442	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		310,117	[1]	271,717	[2]
Total liabilities and stockholders' equity		1,833,695	[1]	1,682,349	[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]	(15,860)		(15,366)
Subtotal assets		(15,860)		(15,366)
Investments in subsidiaries	[5]	(488,557)		(432,277)
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		(504,417)		(447,643)
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]	(15,860)		(15,366)
Total liabilities		(15,860)		(15,366)
Stockholders' equity:
Additional paid-in capital	[5]	(117,601)		(117,601)
Accumulated other comprehensive loss	[5]	(53,516)		(14,115)
Retained earnings	[5]	(311,639)		(294,760)
Unearned employee stock ownership plan shares
Total stockholders' equity		(488,557)		(432,277)
Total liabilities and stockholders' equity		(504,417)		(447,643)
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 June 30, 2016

[2] Balances as of December 31, 2015

[3] Balance for the period ended June 30, 2015

[4] Eliminate intercompany receivables and payables

[5] Eliminate investment in subsidiaries