Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019
ASSETS:
Cash and cash equivalents	$ 825,074	$ 494,352	$ 519,831	$ 673,701
Reinsurance recoverables and trade receivables, net	208,371	186,672
Inventories, net	100,835	101,083
Prepaid expenses	585,879	562,904
Investments, fixed maturities and marketable equities	2,393,522	2,492,738
Investments, other	395,123	360,373
Deferred policy acquisition costs, net	117,123	103,118
Other assets	70,415	71,956
Right of use Assets - Financing	1,026,928	1,080,353
Right of use Assets - Operating	106,682	106,631
Related party assets	9,406	34,784
Subtotal assets	5,839,358	5,594,964
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,043,952	1,032,945
Buildings and improvements	4,752,816	4,663,461
Furniture and equipment	754,641	752,363
Property, plant and equipment (gross)	10,684,750	10,556,222
Less: Accumulated depreciation	(2,811,749)	(2,713,162)
Total property, plant and equipment	7,873,001	7,843,060
Total assets	13,712,359	13,438,024	12,474,744
Liabilities:
Accounts payable and accrued expenses	582,356	554,353
Notes, loans and leases payable	4,777,963	4,621,291
Financing lease liability	666,316
Operating lease liability	106,614	106,443
Policy benefits and losses, claims and loss expenses payable	998,762	997,647
Liabilities from investment contracts	1,833,617	1,802,217
Other policyholders' funds and liabilities	6,764	10,190
Deferred income	42,789	31,620
Deferred income taxes, net	1,106,312	1,093,543
Related party liabilities	0	0
Total liabilities	9,455,177	9,217,304
Stockholders' equity:
Additional paid-in capital	453,819	453,819
Accumulated other comprehensive loss	(13,732)	34,652
Retained earnings	4,484,248	4,399,402
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	4,257,182	4,220,720
Total liabilities and stockholders' equity	13,712,359	13,438,024
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	513,623	511,520
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	3,619,718	3,595,933
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
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	770,941	459,078	500,497	643,918
Reinsurance recoverables and trade receivables, net	83,795	60,073
Inventories, net	100,835	101,083
Prepaid expenses	585,879	562,904
Investments, fixed maturities and marketable equities	0	0
Investments, other	20,988	20,988
Deferred policy acquisition costs, net	0	0
Other assets	67,047	69,128
Right of use Assets - Financing	1,026,928	1,080,353
Right of use Assets - Operating	106,202	106,631
Related party assets	34,035	41,027
Subtotal assets	2,796,650	2,501,265
Investments in subsidiaries	599,538	668,498
Property, plant and equipment, at cost:
Land	1,043,952	1,032,945
Buildings and improvements	4,752,816	4,663,461
Furniture and equipment	754,641	752,363
Property, plant and equipment (gross)	10,684,750	10,556,222
Less: Accumulated depreciation	(2,811,749)	(2,713,162)
Total property, plant and equipment	7,873,001	7,843,060
Total assets	11,269,189	11,012,823
Liabilities:
Accounts payable and accrued expenses	571,473	545,685
Notes, loans and leases payable	4,766,564	4,609,844
Operating lease liability	106,114	106,443
Policy benefits and losses, claims and loss expenses payable	410,989	410,107
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	42,789	31,620
Deferred income taxes, net	1,092,631	1,063,681
Related party liabilities	26,143	24,275
Total liabilities	7,016,703	6,791,655
Stockholders' equity:
Additional paid-in capital	454,029	454,029
Accumulated other comprehensive loss	(18,428)	35,100
Retained earnings	4,484,038	4,399,192
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	4,252,486	4,221,168
Total liabilities and stockholders' equity	11,269,189	11,012,823
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	513,623	511,520
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	3,619,718	3,595,933
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
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	4,119	4,794	6,061	5,757
Reinsurance recoverables and trade receivables, net	87,403	93,995
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	270,083	288,998
Investments, other	96,738	90,145
Deferred policy acquisition costs, net	0	0
Other assets	1,094	680
Right of use Assets - Financing	0	0
Right of use Assets - Operating	262	0
Related party assets	7,024	7,137
Subtotal assets	466,723	485,749
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	466,723	485,749
Liabilities:
Accounts payable and accrued expenses	5,281	5,530
Notes, loans and leases payable	0	0
Operating lease liability	271	0
Policy benefits and losses, claims and loss expenses payable	207,571	210,341
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	1,662	5,751
Deferred income	0	0
Deferred income taxes, net	6,715	8,447
Related party liabilities	3,694	4,616
Total liabilities	225,194	234,685
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	3,937	12,581
Retained earnings	143,171	144,062
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	241,529	251,064
Total liabilities and stockholders' equity	466,723	485,749
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	0	0
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	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	3,301	3,301
Operating Segments [Member] | Property and Casualty Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Life Insurance [Member]
ASSETS:
Cash and cash equivalents	50,014	30,480	13,273	24,026
Reinsurance recoverables and trade receivables, net	37,173	32,604
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,123,439	2,203,740
Investments, other	277,397	249,240
Deferred policy acquisition costs, net	117,123	103,118
Other assets	2,274	2,148
Right of use Assets - Financing	0	0
Right of use Assets - Operating	218	0
Related party assets	13,474	18,629
Subtotal assets	2,621,112	2,639,959
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	2,621,112	2,639,959
Liabilities:
Accounts payable and accrued expenses	5,602	3,138
Notes, loans and leases payable	11,399	11,447
Operating lease liability	229	0
Policy benefits and losses, claims and loss expenses payable	380,202	377,199
Liabilities from investment contracts	1,833,617	1,802,217
Other policyholders' funds and liabilities	5,102	4,439
Deferred income	0	0
Deferred income taxes, net	6,966	21,415
Related party liabilities	1,387	2,670
Total liabilities	2,244,504	2,222,525
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	36,550	78,550
Retained earnings	311,287	310,113
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	376,608	417,434
Total liabilities and stockholders' equity	2,621,112	2,639,959
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	0	0
Operating Segments [Member] | Life Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Operating Segments [Member] | Life Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	2,500	2,500
Operating Segments [Member] | Life Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Life Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Consolidation, Eliminations [Member]
ASSETS:
Cash and cash equivalents	0	0	$ 0	$ 0
Reinsurance recoverables and trade receivables, net	0	0
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	0	0
Investments, other	0	0
Deferred policy acquisition costs, net	0	0
Other assets	0	0
Right of use Assets - Financing	0	0
Right of use Assets - Operating	0	0
Related party assets	(45,127)	(32,009)
Subtotal assets	(45,127)	(32,009)
Investments in subsidiaries	(599,538)	(668,498)
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	(644,665)	(700,507)
Liabilities:
Accounts payable and accrued expenses	0	0
Notes, loans and leases payable	0	0
Operating lease liability	0	0
Policy benefits and losses, claims and loss expenses payable	0	0
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	0	0
Deferred income taxes, net	0	0
Related party liabilities	(31,224)	(31,561)
Total liabilities	(31,224)	(31,561)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	(35,791)	(91,579)
Retained earnings	(454,248)	(453,965)
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	(613,441)	(668,946)
Total liabilities and stockholders' equity	(644,665)	(700,507)
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	0	0
Consolidation, Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Consolidation, Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Consolidation, Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Consolidation, Eliminations [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Consolidation, Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	(5,801)	(5,801)
Consolidation, Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Consolidation, Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	$ 0	$ 0