Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Jun. 30, 2017		Mar. 31, 2017		Jun. 30, 2016	Mar. 31, 2016
ASSETS:
Cash and cash equivalents		$ 803,522		$ 697,806		$ 646,188	$ 600,646
Reinsurance recoverables and trade receivables, net		187,037		178,081
Inventories, net		93,374		82,439
Prepaid expenses		80,118		124,728
Investments, fixed maturities and marketable equities		1,763,031		1,663,768
Investments, other		376,224		367,830
Deferred policy acquisition costs, net		128,878		130,213
Other assets		99,550		97,525
Related party assets		80,865		86,168
Subtotal assets		3,612,599		3,428,558
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		661,622		648,757
Buildings and improvements		2,710,924		2,618,265
Furniture and equipment		529,374		510,415
Property, plant and equipment (gross)		8,646,431		8,361,315
Less: Accumulated depreciation		(2,457,890)		(2,384,033)
Total property, plant and equipment		6,188,541		5,977,282
Total assets		9,801,140		9,405,840		8,543,809
Liabilities:
Accounts payable and accrued expenses		432,122		450,541
Notes, loans and leases payable		3,386,851		3,262,880
Policy benefits and losses, claims and loss expenses payable		1,091,550		1,086,322
Liabilities from investment contracts		1,221,381		1,112,498
Other policyholders' funds and liabilities		14,232		10,150
Deferred income		37,135		28,696
Deferred income taxes, net		854,805		835,009
Related party liabilities
Total liabilities		7,038,076		6,786,096
Stockholders' equity:
Additional paid-in capital		452,319		452,172
Accumulated other comprehensive loss		(35,098)		(51,236)
Retained earnings		3,019,100		2,892,893
Unearned employee stock ownership plan shares		(6,104)		(6,932)
Total stockholders' equity		2,763,064		2,619,744
Total liabilities and stockholders' equity		9,801,140		9,405,840
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		515,733		492,280
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		4,228,778		4,091,598
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Serial 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		748,823		671,665		634,665	585,666
Reinsurance recoverables and trade receivables, net		52,275		41,234
Inventories, net		93,374		82,439
Prepaid expenses		80,118		124,728
Investments, fixed maturities and marketable equities
Investments, other		33,183		35,342
Deferred policy acquisition costs, net
Other assets		96,466		93,197
Related party assets		81,146		88,829
Subtotal assets		1,185,385		1,137,434
Investments in subsidiaries		489,779		477,058
Property, plant and equipment, at cost:
Land		661,622		648,757
Buildings and improvements		2,710,924		2,618,265
Furniture and equipment		529,374		510,415
Property, plant and equipment (gross)		8,646,431		8,361,315
Less: Accumulated depreciation		(2,457,890)		(2,384,033)
Total property, plant and equipment		6,188,541		5,977,282
Total assets		7,863,705		7,591,774
Liabilities:
Accounts payable and accrued expenses		415,785		441,667
Notes, loans and leases payable		3,386,851		3,262,880
Policy benefits and losses, claims and loss expenses payable		406,786		399,181
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		37,135		28,696
Deferred income taxes, net		826,856		809,566
Related party liabilities		27,228		30,040
Total liabilities		5,100,641		4,972,030
Stockholders' equity:
Additional paid-in capital		452,529		452,382
Accumulated other comprehensive loss		(35,098)		(51,236)
Retained earnings		3,018,890		2,892,683
Unearned employee stock ownership plan shares		(6,104)		(6,932)
Total stockholders' equity		2,763,064		2,619,744
Total liabilities and stockholders' equity		7,863,705		7,591,774
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		515,733		492,280
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		4,228,778		4,091,598
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] | Serial 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		8,291	[1]	12,725	[2]	9,439	14,049
Reinsurance recoverables and trade receivables, net		103,382	[1]	107,757	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		259,126	[1]	248,816	[2]
Investments, other		63,337	[1]	63,086	[2]
Deferred policy acquisition costs, net			[1]		[2]
Other assets		589	[1]	1,922	[2]
Related party assets		11,380	[1]	11,496	[2]
Subtotal assets		446,105	[1]	445,802	[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		446,105	[1]	445,802	[2]
Liabilities:
Accounts payable and accrued expenses		3,178	[1]	1,926	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		238,930	[1]	244,980	[2]
Liabilities from investment contracts			[1]		[2]
Other policyholders' funds and liabilities		4,284	[1]	4,184	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		10,924	[1]	11,243	[2]
Related party liabilities		2,421	[1]	2,539	[2]
Total liabilities		259,737	[1]	264,872	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]	91,120	[2]
Accumulated other comprehensive loss		8,030	[1]	6,166	[2]
Retained earnings		83,917	[1]	80,343	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		186,368	[1]	180,930	[2]
Total liabilities and stockholders' equity		446,105	[1]	445,802	[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] | Serial 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		46,408	[1]	13,416	[2]	2,084	931
Reinsurance recoverables and trade receivables, net		31,380	[1]	29,090	[2]
Inventories, net			[1]		[2]
Prepaid expenses			[1]		[2]
Investments, fixed maturities and marketable equities		1,503,905	[1]	1,414,952	[2]
Investments, other		279,704	[1]	269,402	[2]
Deferred policy acquisition costs, net		128,878	[1]	130,213	[2]
Other assets		2,495	[1]	2,406	[2]
Related party assets		18,428	[1]	18,465	[2]
Subtotal assets		2,011,198	[1]	1,877,944	[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		2,011,198	[1]	1,877,944	[2]
Liabilities:
Accounts payable and accrued expenses		13,159	[1]	6,948	[2]
Notes, loans and leases payable			[1]		[2]
Policy benefits and losses, claims and loss expenses payable		445,834	[1]	442,161	[2]
Liabilities from investment contracts		1,221,381	[1]	1,112,498	[2]
Other policyholders' funds and liabilities		9,948	[1]	5,966	[2]
Deferred income			[1]		[2]
Deferred income taxes, net		17,025	[1]	14,200	[2]
Related party liabilities		440	[1]	43	[2]
Total liabilities		1,707,787	[1]	1,581,816	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]	26,271	[2]
Accumulated other comprehensive loss		21,980	[1]	16,933	[2]
Retained earnings		252,660	[1]	250,424	[2]
Unearned employee stock ownership plan shares			[1]		[2]
Total stockholders' equity		303,411	[1]	296,128	[2]
Total liabilities and stockholders' equity		2,011,198	[1]	1,877,944	[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] | Serial 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]	(30,089)		(32,622)
Subtotal assets		(30,089)		(32,622)
Investments in subsidiaries	[4]	(489,779)		(477,058)
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		(519,868)		(509,680)
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]	(30,089)		(32,622)
Total liabilities		(30,089)		(32,622)
Stockholders' equity:
Additional paid-in capital	[4]	(117,601)		(117,601)
Accumulated other comprehensive loss	[4]	(30,010)		(23,099)
Retained earnings	[4]	(336,367)		(330,557)
Unearned employee stock ownership plan shares
Total stockholders' equity		(489,779)		(477,058)
Total liabilities and stockholders' equity		(519,868)		(509,680)
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] | Serial 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, 2017

[2] Balances as of December 31, 2016

[3] Eliminate intercompany receivables and payables

[4] Eliminate investment in subsidiaries