Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015
ASSETS:
Cash and cash equivalents		$ 984,185		$ 600,646		$ 674,627		$ 441,850
Reinsurance recoverables and trade receivables, net		199,095		175,210
Inventories, net		79,682		79,756
Prepaid expenses		54,486		134,300
Investments, fixed maturities and marketable equities		1,700,581		1,510,538
Investments, other		376,813		310,072
Deferred policy acquisition costs, net		118,040		136,386
Other assets		78,049		77,210
Related party assets		91,705		85,734
Subtotal assets		3,682,636		3,109,852
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		633,725		587,347
Buildings and improvements		2,509,073		2,187,400
Furniture and equipment		477,131		399,943
Property, plant and equipment, gross		7,919,530		7,151,244
Less: Accumulated depreciation		(2,314,849)		(2,133,733)
Total property, plant and equipment		5,604,681		5,017,511
Total assets		9,287,317		8,127,363		7,762,534
Liabilities:
Accounts payable and accrued expenses		435,000		502,613
Notes, loans and leases payable		3,198,435		2,665,396
Policy benefits and losses, claims and loss expenses payable		1,083,627		1,071,412
Liabilities from investment contracts		1,085,775		951,490
Other policyholders' funds and liabilities		8,268		8,650
Deferred income		23,847		22,784
Deferred income taxes, net		791,661		653,612
Related party liabilities
Total liabilities		6,626,613		5,875,957
Stockholders' equity:
Additional paid-in capital		452,014		451,629
Accumulated other comprehensive loss		(21,034)		(60,525)
Retained earnings		2,902,932		2,533,641
Unearned employee stock ownership plan shares		(6,055)		(6,186)
Total stockholders' equity		2,660,704		2,251,406
Total liabilities and stockholders' equity		9,287,317		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		493,214		462,379
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		3,806,387		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		971,002		585,666		649,191		431,873
Reinsurance recoverables and trade receivables, net		58,514		34,451
Inventories, net		79,682		79,756
Prepaid expenses		54,486		134,300
Investments, fixed maturities and marketable equities
Investments, other		29,694		21,431
Deferred policy acquisition costs, net
Other assets		74,960		71,719
Related party assets		93,873		88,022
Subtotal assets		1,362,211		1,015,345
Investments in subsidiaries		500,358		432,277
Property, plant and equipment, at cost:
Land		633,725		587,347
Buildings and improvements		2,509,073		2,187,400
Furniture and equipment		477,131		399,943
Property, plant and equipment, gross		7,919,530		7,151,244
Less: Accumulated depreciation		(2,314,849)		(2,133,733)
Total property, plant and equipment		5,604,681		5,017,511
Total assets		7,467,250		6,465,133
Liabilities:
Accounts payable and accrued expenses		424,621		492,982
Notes, loans and leases payable		3,198,435		2,665,396
Policy benefits and losses, claims and loss expenses payable		397,542		386,366
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		23,847		22,784
Deferred income taxes, net		749,979		633,061
Related party liabilities		12,122		13,138
Total liabilities		4,806,546		4,213,727
Stockholders' equity:
Additional paid-in capital		452,224		451,839
Accumulated other comprehensive loss		(21,034)		(60,525)
Retained earnings		2,902,722		2,533,431
Unearned employee stock ownership plan shares		(6,055)		(6,186)
Total stockholders' equity		2,660,704		2,251,406
Total liabilities and stockholders' equity		7,467,250		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		493,214		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		3,806,387		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		11,258	[1]	14,049	[2]	13,882	[3]	8,495	[3]
Reinsurance recoverables and trade receivables, net		109,590	[1]	111,978	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		249,780	[1]	238,570	[2]
Investments, other		68,997	[1]	47,374	[2]
Deferred policy acquisition costs, net			[1]		[2]
Other assets		768	[1]	3,088	[2]
Related party assets		12,290	[1]	12,465	[2]
Subtotal assets		452,683	[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		452,683	[1]	427,524	[2]
Liabilities:
Accounts payable and accrued expenses		3,899	[1]	1,535	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		247,169	[1]	252,819	[2]
Liabilities from investment contracts			[1]		[2]
Other policyholders' funds and liabilities		4,040	[1]	3,017	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		11,542	[1]	7,526	[2]
Related party liabilities		2,700	[1]	2,067	[2]
Total liabilities		269,350	[1]	266,964	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]	91,120	[2]
Accumulated other comprehensive loss		12,088	[1]	3,611	[2]
Retained earnings		76,824	[1]	62,528	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		183,333	[1]	160,560	[2]
Total liabilities and stockholders' equity		452,683	[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		1,925	[1]	931	[2]	11,554	[3]	1,482	[3]
Reinsurance recoverables and trade receivables, net		30,991	[1]	28,781	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		1,450,801	[1]	1,271,968	[2]
Investments, other		278,122	[1]	241,267	[2]
Deferred policy acquisition costs, net		118,040	[1]	136,386	[2]
Other assets		2,321	[1]	2,403	[2]
Related party assets		461	[1]	613	[2]
Subtotal assets		1,882,661	[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		1,882,661	[1]	1,682,349	[2]
Liabilities:
Accounts payable and accrued expenses		6,480	[1]	8,096	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		438,916	[1]	432,227	[2]
Liabilities from investment contracts		1,085,775	[1]	951,490	[2]
Other policyholders' funds and liabilities		4,228	[1]	5,633	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		30,140	[1]	13,025	[2]
Related party liabilities		97	[1]	161	[2]
Total liabilities		1,565,636	[1]	1,410,632	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]	26,271	[2]
Accumulated other comprehensive loss		44,183	[1]	10,504	[2]
Retained earnings		244,071	[1]	232,442	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		317,025	[1]	271,717	[2]
Total liabilities and stockholders' equity		1,882,661	[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]	(14,919)		(15,366)
Subtotal assets		(14,919)		(15,366)
Investments in subsidiaries	[5]	(500,358)		(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		(515,277)		(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]	(14,919)		(15,366)
Total liabilities		(14,919)		(15,366)
Stockholders' equity:
Additional paid-in capital	[5]	(117,601)		(117,601)
Accumulated other comprehensive loss	[5]	(56,271)		(14,115)
Retained earnings	[5]	(320,685)		(294,760)
Unearned employee stock ownership plan shares
Total stockholders' equity		(500,358)		(432,277)
Total liabilities and stockholders' equity		(515,277)		(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 September 30, 2016

[2] Balances as of December 31, 2015

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

[4] Eliminate intercompany receivables and payables

[5] Eliminate investment in subsidiaries