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Borrowings (Narratives) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
Borrowings (Narratives) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 3,422,077			$ 3,422,077		$ 3,262,880
Interest paid related to derivative contracts [Abstract]
Interest paid in cash	32,400		$ 28,100	63,400	$ 55,300
Real estate loan [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	140,287			140,287		169,289
Senior Mortgages [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	1,405,702			1,405,702		1,292,160
Working Capital Loans [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	55,000			55,000		85,000
Rental Truck (amortizing loans) First Loan [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	319,631			319,631		324,977
Fleet Loan Securitization [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	47,183			47,183		52,112
Capital Lease Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	962,140			962,140		876,828
Capital Lease Obligations [Member] \| AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	962,100			962,100		876,800
New capital lease obligations, amount				233,900
Capitalized assets, net book value	1,367,000			$ 1,367,000		1,233,300
Debt instruments, miscellaneous information:
Terms of lease				Between 5 and 7 years
Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 72,005			$ 72,005		$ 69,867
Amerco Real Estate Subsidiaries and Uhaul Company of Florida [Member] \| Real estate loan [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	6.93%			6.93%
Debt instruments, interest rate, effective percentage:
LIBOR	1.24%			1.24%
Applicable margin interest rate	1.50%			1.50%
Sum of LIBOR and margin, maximum rate	2.74%			2.74%
Debt instruments, face, payment, and remaining balance amount:
Line of credit facility, remaining borrowing capacity	$ 63,100			$ 63,100
Amounts held at LIBOR plus margin	77,200			77,200
Notes, loans and leases payable	140,300			$ 140,300
Debt instruments, issuance and maturity dates:
Mortgage loans on real estate, final maturity date				Apr. 30, 2023
Debt instrument, maturity date				Aug. 31, 2018
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Senior Mortgages [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 1,405,700			$ 1,405,700
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jan. 01, 2022
Debt instrument, maturity date range, end				Dec. 31, 2038
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Senior Mortgages [Member] \| Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	3.72%			3.72%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Senior Mortgages [Member] \| Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	5.50%			5.50%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Working Capital Loans [Member] \| AMERCO [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	1.24%			1.24%
Applicable margin interest rate	1.50%			1.50%
Sum of LIBOR and margin, maximum rate	2.74%			2.74%
Debt instruments, face, payment, and remaining balance amount:
Line of credit facility, maximum borrowing capacity	$ 55,000			$ 55,000
Line of credit, current borrowing capacity	55,000			$ 55,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date				Nov. 30, 2018
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Working Capital Loans Two [Member] \| AMERCO [Member]
Debt instruments, interest rate, effective percentage:
Unused capacity fee				0.30%
Debt instruments, face, payment, and remaining balance amount:
Line of credit facility, maximum borrowing capacity	300,000			$ 300,000
Line of credit, current borrowing capacity	150,000			150,000
Line of credit facility, remaining borrowing capacity	$ 150,000			$ 150,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date				Sep. 30, 2020
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Working Capital Loans Two [Member] \| AMERCO [Member] \| Minimum [Member]
Debt instruments, interest rate, effective percentage:
Sum of LIBOR and margin, maximum rate	1.38%			1.38%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Working Capital Loans Two [Member] \| AMERCO [Member] \| Maximum [Member]
Debt instruments, interest rate, effective percentage:
Sum of LIBOR and margin, maximum rate	1.50%			1.50%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] \| Revolving fleet loans [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	1.24%			1.24%
Applicable margin interest rate	1.15%			1.15%
Sum of LIBOR and margin, maximum rate	2.39%			2.39%
Debt instruments, face, payment, and remaining balance amount:
Debt instrument, original face amount	$ 490,000			$ 490,000
Line of credit facility, maximum borrowing capacity	565,000			565,000
Notes, loans and leases payable	446,000			$ 446,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Mar. 01, 2020
Debt instrument, maturity date range, end				Nov. 30, 2021
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) First Loan [Member] \| AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 319,600			$ 319,600
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jun. 01, 2018
Debt instrument, maturity date range, end				Jun. 30, 2024
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) First Loan [Member] \| AMERCO [Member] \| Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.82%			2.82%
Debt instruments, interest rate, effective percentage:
LIBOR	1.23%			1.23%
Applicable margin interest rate	1.72%			1.72%
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) First Loan [Member] \| AMERCO [Member] \| Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	4.76%			4.76%
Debt instruments, interest rate, effective percentage:
LIBOR	1.24%			1.24%
Applicable margin interest rate	2.38%			2.38%
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) Second loan [Member] \| AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 260,700			$ 260,700
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) Second loan [Member] \| AMERCO [Member] \| Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.95%			1.95%
Uhaul Intl and Subsidiaries [Member] \| Rental Truck (amortizing loans) Second loan [Member] \| AMERCO [Member] \| Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	3.94%			3.94%
Uhaul S Fleet Two Thousand Ten Box Truck Note [Member] \| Fleet Loan Securitization [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	4.90%			4.90%
Debt instruments, face, payment, and remaining balance amount:
Debt instrument, original face amount	$ 155,000			$ 155,000
Notes, loans and leases payable	47,200			$ 47,200
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date				Oct. 31, 2017
Amerco, Us Bank, National Association, Trustee [Member] \| Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	76,100			$ 76,100
Subsidiary holdings of parent company debt	$ 4,100			$ 4,100
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jan. 01, 2017
Debt instrument, maturity date range, end				Dec. 31, 2047
Amerco, Us Bank, National Association, Trustee [Member] \| Other Obligations [Member] \| Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.75%			2.75%
Amerco, Us Bank, National Association, Trustee [Member] \| Other Obligations [Member] \| Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	8.00%			8.00%
Life Insurance [Member] \| Federal Home Loan Bank [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Initial deposit amount		$ 45,000
Initial deposit interest rate		1.00%
Initial deposit maturity date		Sep. 29, 2017
Additional deposit amount		$ 15,000
Additional deposit interest rate		1.75%
Additional advance maturity date		Mar. 30, 2020
Available for sale equity securities, noncurrent		$ 130,200
Available for sale equity securities pledged as collateral		$ 69,300