Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Mar. 31, 2019
ASSETS:
Cash and cash equivalents	$ 2,704,137		$ 1,194,012		$ 494,352	$ 673,701
Reinsurance recoverables and trade receivables, net	229,343		224,426
Inventories, net	158,888		105,577
Prepaid expenses	236,915		469,144
Investments, fixed maturities and marketable equities	2,893,399		2,695,656
Investments, other	543,755		489,759
Deferred policy acquisition costs, net	103,828		89,749
Other assets	60,409		47,730
Right of use assets, financing, net	620,824		877,038
Right of use assets, operating	74,382		92,505
Related party assets	47,851		35,395
Subtotal assets	7,673,731		6,320,991
Investments in subsidiaries	0		0
Property, plant and equipment, at cost:
Land	1,283,142		1,075,813
Buildings and improvements	5,974,639		5,163,705
Furniture and equipment	846,132		786,505
Property, plant and equipment (gross)	13,358,406		11,413,668
Less: Accumulated depreciation	(3,732,556)		(3,083,053)
Total property, plant and equipment	9,625,850		8,330,615
Total assets	17,299,581		14,651,606		13,438,024
Liabilities:
Accounts payable and accrued expenses	677,785		645,575
Notes, loans and leases payable	6,022,497		4,668,907
Operating lease liabilities	74,197		92,510
Policy benefits and losses, claims and loss expenses payable	978,254		997,701
Liabilities from investment contracts	2,336,238		2,161,530
Other policyholders' funds and liabilities	10,812		12,420
Deferred income	49,157		42,592
Deferred income taxes	1,265,358		1,178,489
Related party liabilities	0		0
Total liabilities	11,414,298		9,799,724
Stockholders' equity:
Additional paid-in capital	453,819		453,819
Accumulated other comprehensive loss	46,384		106,857
Retained earnings	6,052,233		4,958,359
Total stockholders' equity	5,885,283		4,851,882
Total liabilities and stockholders' equity	17,299,581		14,651,606
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	615,679		477,921
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	4,638,814		3,909,724
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
Series A 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	2,643,213		1,010,275		459,078	643,918
Reinsurance recoverables and trade receivables, net	142,895		118,741
Inventories, net	158,888		105,577
Prepaid expenses	236,915		469,144
Investments, fixed maturities and marketable equities	0		0
Investments, other	20,653		20,733
Deferred policy acquisition costs, net	0		0
Other assets	57,305		44,763
Right of use assets, financing, net	620,824		877,038
Right of use assets, operating	74,190		92,245
Related party assets	64,611		54,042
Subtotal assets	4,019,494		2,792,558
Investments in subsidiaries	737,073		741,860
Property, plant and equipment, at cost:
Land	1,283,142		1,075,813
Buildings and improvements	5,974,639		5,163,705
Furniture and equipment	846,132		786,505
Property, plant and equipment (gross)	13,358,406		11,413,668
Less: Accumulated depreciation	(3,732,556)		(3,083,053)
Total property, plant and equipment	9,625,850		8,330,615
Total assets	14,382,417		11,865,033
Liabilities:
Accounts payable and accrued expenses	663,482		636,257
Notes, loans and leases payable	6,022,497		4,657,720
Operating lease liabilities	73,998		92,236
Policy benefits and losses, claims and loss expenses payable	418,890		427,073
Liabilities from investment contracts	0		0
Other policyholders' funds and liabilities	0		0
Deferred income	49,157		42,592
Deferred income taxes	1,244,639		1,136,149
Related party liabilities	25,668		25,413
Total liabilities	8,498,331		7,017,440
Stockholders' equity:
Additional paid-in capital	454,029		454,029
Accumulated other comprehensive loss	45,187		102,568
Retained earnings	6,052,023		4,958,149
Total stockholders' equity	5,884,086		4,847,593
Total liabilities and stockholders' equity	14,382,417		11,865,033
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	615,679		477,921
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	4,638,814		3,909,724
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] | Series A 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	10,800		5,658		4,794	5,757
Reinsurance recoverables and trade receivables, net	50,235		67,069
Inventories, net	0		0
Prepaid expenses	0		0
Investments, fixed maturities and marketable equities	297,488		295,753
Investments, other	114,269		90,412
Deferred policy acquisition costs, net	0		0
Other assets	371		436
Right of use assets, financing, net	0		0
Right of use assets, operating	93		92
Related party assets	6,713		6,854
Subtotal assets	479,969		466,274
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	479,969		466,274
Liabilities:
Accounts payable and accrued expenses	3,849		2,029
Notes, loans and leases payable	0		0
Operating lease liabilities	93		96
Policy benefits and losses, claims and loss expenses payable	160,379	$ 160,379	178,942	$ 178,942
Liabilities from investment contracts	0		0
Other policyholders' funds and liabilities	3,521		3,698
Deferred income	0		0
Deferred income taxes	12,803		13,046
Related party liabilities	3,196		5,821
Total liabilities	183,841		203,632
Stockholders' equity:
Additional paid-in capital	91,120		91,120
Accumulated other comprehensive loss	16,630		22,546
Retained earnings	185,077		145,675
Total stockholders' equity	296,128		262,642
Total liabilities and stockholders' equity	479,969		466,274
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] | Series A 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	50,124		178,079		30,480	24,026
Reinsurance recoverables and trade receivables, net	36,213		38,616
Inventories, net	0		0
Prepaid expenses	0		0
Investments, fixed maturities and marketable equities	2,595,911		2,399,903
Investments, other	408,833		378,614
Deferred policy acquisition costs, net	103,828		89,749
Other assets	2,733		2,531
Right of use assets, financing, net	0		0
Right of use assets, operating	99		168
Related party assets	16,911		13,850
Subtotal assets	3,214,652		3,101,510
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	3,214,652		3,101,510
Liabilities:
Accounts payable and accrued expenses	10,454		7,289
Notes, loans and leases payable	0		11,187
Operating lease liabilities	106		178
Policy benefits and losses, claims and loss expenses payable	398,985		391,686
Liabilities from investment contracts	2,336,238		2,161,530
Other policyholders' funds and liabilities	7,291		8,722
Deferred income	0		0
Deferred income taxes	7,916		29,294
Related party liabilities	12,717		12,406
Total liabilities	2,773,707		2,622,292
Stockholders' equity:
Additional paid-in capital	26,271		26,271
Accumulated other comprehensive loss	87,200		140,817
Retained earnings	324,974		309,630
Total stockholders' equity	440,945		479,218
Total liabilities and stockholders' equity	3,214,652		3,101,510
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] | Series A 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
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, net	0		0
Right of use assets, operating	0		0
Related party assets	(40,384)		(39,351)
Subtotal assets	(40,384)		(39,351)
Investments in subsidiaries	(737,073)		(741,860)
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	(777,457)		(781,211)
Liabilities:
Accounts payable and accrued expenses	0		0
Notes, loans and leases payable	0		0
Operating lease liabilities	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	0		0
Related party liabilities	(41,581)		(43,640)
Total liabilities	(41,581)		(43,640)
Stockholders' equity:
Additional paid-in capital	(117,601)		(117,601)
Accumulated other comprehensive loss	(102,633)		(159,074)
Retained earnings	(509,841)		(455,095)
Total stockholders' equity	(735,876)		(737,571)
Total liabilities and stockholders' equity	(777,457)		(781,211)
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
Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0		0
Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0		0
Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0		0
Eliminations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0		0
Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	(5,801)		(5,801)
Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0		0
Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	$ 0		$ 0