Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018
ASSETS:
Cash and cash equivalents	$ 525,231	$ 673,701	$ 652,440	$ 759,388
Reinsurance recoverables and trade receivables, net	222,481	224,785
Inventories, net	102,357	103,504
Prepaid expenses	194,250	174,100
Investments, fixed maturities and marketable equities	2,413,350	2,235,397
Investments, other	320,992	300,736
Deferred policy acquisition costs, net	111,708	136,276
Right of use Assets - Financing	72,432	78,354
Right of use Assets - Operating	1,185,629	0
Other assets	105,298
Related party assets	12,902	30,889
Subtotal assets	5,266,630	3,957,742
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,016,918	976,454
Buildings and improvements	4,371,637	4,003,726
Furniture and equipment	716,287	689,780
Property, plant and equipment (gross)	10,160,140	11,022,027
Less: Accumulated depreciation	(2,570,568)	(3,088,056)
Total property, plant and equipment	7,589,572	7,933,971
Total assets	12,856,202	11,891,713	11,323,845
Liabilities:
Accounts payable and accrued expenses	546,260	556,873
Notes, loans and leases payable	4,497,912	4,163,323
Financing lease liability	861,751
Operating lease liability	104,832	0
Policy benefits and losses, claims and loss expenses payable	1,022,134	1,011,183
Liabilities from investment contracts	1,720,995	1,666,742
Other policyholders' funds and liabilities	10,911	15,047
Deferred income	35,926	35,186
Deferred income taxes, net	859,164	750,970
Related party liabilities	0	0
Total liabilities	8,798,134	8,199,324
Stockholders' equity:
Additional paid-in capital	453,761	453,326
Accumulated other comprehensive loss	17,151	(66,698)
Retained earnings	4,255,906	3,976,962
Unearned employee stock ownership plan shares		(4,048)
Total stockholders' equity	4,058,068	3,692,389
Total liabilities and stockholders' equity	12,856,202	11,891,713
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	495,264	590,039
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	3,560,034	4,762,028
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)
Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(151,997)
Operating Segments [Member] | Moving and Storage Consolidations [Member]
ASSETS:
Cash and cash equivalents	498,984	643,918	618,163	702,036
Reinsurance recoverables and trade receivables, net	91,985	90,832
Inventories, net	102,357	103,504
Prepaid expenses	194,250	174,100
Investments, fixed maturities and marketable equities	0	0
Investments, other	20,988	23,013
Deferred policy acquisition costs, net	0	0
Right of use Assets - Financing	68,416
Right of use Assets - Operating	1,185,629
Other assets	105,298	72,768
Related party assets	38,671	35,997
Subtotal assets	2,306,578	1,144,132
Investments in subsidiaries	619,513	534,157
Property, plant and equipment, at cost:
Land	1,016,918	976,454
Buildings and improvements	4,371,637	4,003,726
Furniture and equipment	716,287	689,780
Property, plant and equipment (gross)	10,160,140	11,022,027
Less: Accumulated depreciation	(2,570,568)	(3,088,056)
Total property, plant and equipment	7,589,572	7,933,971
Total assets	10,515,663	9,612,260
Liabilities:
Accounts payable and accrued expenses	538,687	548,099
Notes, loans and leases payable	4,497,912	4,163,323
Operating lease liability	104,832
Policy benefits and losses, claims and loss expenses payable	425,448	407,934
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	35,926	35,186
Deferred income taxes, net	828,584	741,644
Related party liabilities	25,851	25,446
Total liabilities	6,457,240	5,921,632
Stockholders' equity:
Additional paid-in capital	453,971	453,536
Accumulated other comprehensive loss	17,506	(68,459)
Retained earnings	4,255,696	3,976,752
Unearned employee stock ownership plan shares	(1,597)	(4,048)
Total stockholders' equity	4,058,423	3,690,628
Total liabilities and stockholders' equity	10,515,663	9,612,260
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	495,264	590,039
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	3,560,034	4,762,028
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	11,576	5,757	7,247	6,639
Reinsurance recoverables and trade receivables, net	96,690	102,120
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	294,681	279,641
Investments, other	82,395	74,679
Deferred policy acquisition costs, net	0	0
Right of use Assets - Financing	880
Right of use Assets - Operating	0
Other assets	0	2,456
Related party assets	8,998	6,639
Subtotal assets	495,220	471,292
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	495,220	471,292
Liabilities:
Accounts payable and accrued expenses	2,865	2,844
Notes, loans and leases payable	0	0
Operating lease liability	0
Policy benefits and losses, claims and loss expenses payable	223,744	229,958
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	5,641	5,259
Deferred income	0	0
Deferred income taxes, net	9,068	6,961
Related party liabilities	4,216	3,836
Total liabilities	245,534	248,858
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	9,615	(3,721)
Retained earnings	145,650	131,734
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	249,686	222,434
Total liabilities and stockholders' equity	495,220	471,292
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	14,671	24,026	27,030	50,713
Reinsurance recoverables and trade receivables, net	33,806	31,833
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,118,669	1,955,756
Investments, other	217,609	203,044
Deferred policy acquisition costs, net	111,708	136,276
Right of use Assets - Financing	3,136
Right of use Assets - Operating	0
Other assets	0	3,130
Related party assets	18,554	16,466
Subtotal assets	2,518,153	2,370,531
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	2,518,153	2,370,531
Liabilities:
Accounts payable and accrued expenses	4,708	5,930
Notes, loans and leases payable	0	0
Operating lease liability	0
Policy benefits and losses, claims and loss expenses payable	372,942	373,291
Liabilities from investment contracts	1,720,995	1,666,742
Other policyholders' funds and liabilities	5,270	9,788
Deferred income	0	0
Deferred income taxes, net	21,512	2,365
Related party liabilities	1,299	692
Total liabilities	2,126,726	2,058,808
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	65,575	(5,300)
Retained earnings	297,081	288,252
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	391,427	311,723
Total liabilities and stockholders' equity	2,518,153	2,370,531
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
Right of use Assets - Financing	0
Right of use Assets - Operating	0
Other assets	0	0
Related party assets	(53,321)	(28,213)
Subtotal assets	(53,321)	(28,213)
Investments in subsidiaries	(619,513)	(534,157)
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	(672,834)	(562,370)
Liabilities:
Accounts payable and accrued expenses	0	0
Notes, loans and leases payable	0	0
Operating lease liability	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	(31,366)	(29,974)
Total liabilities	(31,366)	(29,974)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	(75,545)	10,782
Retained earnings	(442,521)	(419,776)
Unearned employee stock ownership plan shares	0	0
Total stockholders' equity	(641,468)	(532,396)
Total liabilities and stockholders' equity	(672,834)	(562,370)
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