Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Jun. 30, 2016		Mar. 31, 2016		Jun. 30, 2015	Mar. 31, 2015
ASSETS:
Cash and cash equivalents		$ 646,188		$ 600,646		$ 475,562	$ 441,850
Reinsurance recoverables and trade receivables, net		189,317		175,210
Inventories, net		82,923		79,756
Prepaid expenses		94,540		134,300
Investments, fixed maturities and marketable equities		1,656,159		1,510,538
Investments, other		280,860		310,072
Deferred policy acquisition costs, net		126,830		136,386
Other assets		80,467		77,210
Related party assets		80,812		85,734
Subtotal assets		3,238,096		3,109,852
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		603,246		587,347
Buildings and improvements		2,289,715		2,187,400
Furniture and equipment		422,404		399,943
Property, plant and equipment (gross)		7,497,220		7,151,244
Less: Accumulated depreciation		(2,191,507)		(2,133,733)
Total property, plant and equipment		5,305,713		5,017,511
Total assets		8,543,809		8,127,363		7,090,634
Liabilities:
Accounts payable and accrued expenses		480,116		502,613
Notes, loans and leases payable		2,827,052		2,665,396
Policy benefits and losses, claims and loss expenses payable		1,072,728		1,071,412
Liabilities from investment contracts		1,016,653		951,490
Other policyholders' funds and liabilities		8,891		8,650
Deferred income		31,506		22,784
Deferred income taxes, net		687,576		653,612
Related party liabilities
Total liabilities		6,124,522		5,875,957
Stockholders' equity:
Additional paid-in capital		451,773		451,629
Accumulated other comprehensive loss		(40,125)		(60,525)
Retained earnings		2,680,814		2,533,641
Unearned employee stock ownership plan shares		(6,022)		(6,186)
Total stockholders' equity		2,419,287		2,251,406
Total liabilities and stockholders' equity		8,543,809		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		479,071		462,379
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		3,702,784		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		634,665		585,666		459,636	431,873
Reinsurance recoverables and trade receivables, net		45,166		34,451
Inventories, net		82,923		79,756
Prepaid expenses		94,540		134,300
Investments, fixed maturities and marketable equities
Investments, other		23,274		21,431
Deferred policy acquisition costs, net
Other assets		77,372		71,719
Related party assets		84,329		88,022
Subtotal assets		1,042,269		1,015,345
Investments in subsidiaries		459,239		432,277
Property, plant and equipment, at cost:
Land		603,246		587,347
Buildings and improvements		2,289,715		2,187,400
Furniture and equipment		422,404		399,943
Property, plant and equipment (gross)		7,497,220		7,151,244
Less: Accumulated depreciation		(2,191,507)		(2,133,733)
Total property, plant and equipment		5,305,713		5,017,511
Total assets		6,807,221		6,465,133
Liabilities:
Accounts payable and accrued expenses		474,414		492,982
Notes, loans and leases payable		2,827,052		2,665,396
Policy benefits and losses, claims and loss expenses payable		384,710		386,366
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		31,506		22,784
Deferred income taxes, net		656,252		633,061
Related party liabilities		14,000		13,138
Total liabilities		4,387,934		4,213,727
Stockholders' equity:
Additional paid-in capital		451,983		451,839
Accumulated other comprehensive loss		(40,125)		(60,525)
Retained earnings		2,680,604		2,533,431
Unearned employee stock ownership plan shares		(6,022)		(6,186)
Total stockholders' equity		2,419,287		2,251,406
Total liabilities and stockholders' equity		6,807,221		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		479,071		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		3,702,784		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		9,439	[1]	14,049	[2]	10,091	8,495
Reinsurance recoverables and trade receivables, net		112,399	[1]	111,978	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		248,016	[1]	238,570	[2]
Investments, other		53,775	[1]	47,374	[2]
Deferred policy acquisition costs, net			[1]		[2]
Other assets		740	[1]	3,088	[2]
Related party assets		12,326	[1]	12,465	[2]
Subtotal assets		436,695	[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		436,695	[1]	427,524	[2]
Liabilities:
Accounts payable and accrued expenses		1,396	[1]	1,535	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		251,072	[1]	252,819	[2]
Liabilities from investment contracts			[1]		[2]
Other policyholders' funds and liabilities		3,024	[1]	3,017	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		9,586	[1]	7,526	[2]
Related party liabilities		2,317	[1]	2,067	[2]
Total liabilities		267,395	[1]	266,964	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]	91,120	[2]
Accumulated other comprehensive loss		7,474	[1]	3,611	[2]
Retained earnings		67,405	[1]	62,528	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		169,300	[1]	160,560	[2]
Total liabilities and stockholders' equity		436,695	[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		2,084	[1]	931	[2]	5,835	1,482
Reinsurance recoverables and trade receivables, net		31,752	[1]	28,781	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		1,408,143	[1]	1,271,968	[2]
Investments, other		203,811	[1]	241,267	[2]
Deferred policy acquisition costs, net		126,830	[1]	136,386	[2]
Other assets		2,355	[1]	2,403	[2]
Related party assets		562	[1]	613	[2]
Subtotal assets		1,775,537	[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		1,775,537	[1]	1,682,349	[2]
Liabilities:
Accounts payable and accrued expenses		4,306	[1]	8,096	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		436,946	[1]	432,227	[2]
Liabilities from investment contracts		1,016,653	[1]	951,490	[2]
Other policyholders' funds and liabilities		5,867	[1]	5,633	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		21,738	[1]	13,025	[2]
Related party liabilities		88	[1]	161	[2]
Total liabilities		1,485,598	[1]	1,410,632	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]	26,271	[2]
Accumulated other comprehensive loss		26,029	[1]	10,504	[2]
Retained earnings		235,139	[1]	232,442	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		289,939	[1]	271,717	[2]
Total liabilities and stockholders' equity		1,775,537	[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	[3]	(16,405)		(15,366)
Subtotal assets		(16,405)		(15,366)
Investments in subsidiaries	[4]	(459,239)		(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		(475,644)		(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	[3]	(16,405)		(15,366)
Total liabilities		(16,405)		(15,366)
Stockholders' equity:
Additional paid-in capital	[4]	(117,601)		(117,601)
Accumulated other comprehensive loss	[4]	(33,503)		(14,115)
Retained earnings	[4]	(302,334)		(294,760)
Unearned employee stock ownership plan shares
Total stockholders' equity		(459,239)		(432,277)
Total liabilities and stockholders' equity		(475,644)		(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	[4]	(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 March 31, 2016

[2] Balances as of December 31, 2015

[3] Eliminate intercompany receivables and payables

[4] Eliminate investment in subsidiaries