Borrowings (Narratives) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		$ 4,163,323	$ 3,513,076
Real estate loan (amortizing term) [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		$ 102,913	135,287
Real estate loan (amortizing term) [Member] | Minimum [Member]
Debt instruments, issuance and maturity dates:
Mortgage loans on real estate, final maturity date		Jan. 01, 2019
Real estate loan (amortizing term) [Member] | Maximum [Member]
Debt instruments, issuance and maturity dates:
Mortgage loans on real estate, final maturity date		Dec. 31, 2036
Senior mortgages [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		$ 1,741,652	1,487,645
Real estate loans (revolving credit) [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		429,400	55,000
Rental Truck (amortizing loans) First Loan [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		263,209	342,971
Capital Lease Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		1,042,652	984,217
Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		$ 82,417	73,579
Amerco Real Estate Subsidiaries and Uhaul Company of Florida [Member] | Real estate loan (amortizing term) [Member]
Debt instruments, interest rate, effective percentage:
LIBOR		2.49%
Applicable margin interest rate		1.50%
Sum of LIBOR and margin, maximum rate		3.99%
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%
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		6.62%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Real estate loans (revolving credit) [Member] | Amerco [Member]
Debt instruments, face, payment, and remaining balance amount:
Aggregate borrowing capacity, amount		$ 335,000
Notes, loans and leases payable		$ 329,400
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start		Jun. 01, 2021
Debt instrument, maturity date range, end		Feb. 28, 2024
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Real estate loans (revolving credit) [Member] | Amerco [Member] | Minimum [Member]
Debt instruments, interest rate, effective percentage:
LIBOR		2.49%
Applicable margin interest rate		1.25%
Sum of LIBOR and margin, maximum rate		3.74%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Real estate loans (revolving credit) [Member] | Amerco [Member] | Maximum [Member]
Debt instruments, interest rate, effective percentage:
LIBOR		2.50%
Applicable margin interest rate		1.50%
Sum of LIBOR and margin, maximum rate		3.99%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Real estate loans two (revolving credit) [Member] | Amerco [Member]
Debt instruments, interest rate, effective percentage:
LIBOR		2.49%
Applicable margin interest rate		1.38%
Sum of LIBOR and margin, maximum rate		3.87%
Unused capacity fee		0.30%
Debt instruments, face, payment, and remaining balance amount:
Debt instrument, original face amount		$ 150,000
Line of credit facility, maximum borrowing capacity		300,000
Notes, loans and leases payable		$ 100,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date		Sep. 30, 2021
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%
Debt instruments, interest rate, effective percentage:
LIBOR		2.48%
Applicable margin interest rate		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		3.00%
Debt instruments, interest rate, effective percentage:
LIBOR		2.49%
Applicable margin interest rate		1.75%
Uhaul Intl and Subsidiaries [Member] | Rental Truck (amortizing loans) Second Loan [Member] | Amerco [Member]
Debt instruments, face, payment, and remaining balance amount:
Amount held at fixed interest rate		$ 241,400
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%
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		4.66%
Uhaul Intl and Subsidiaries [Member] | Rental Truck Revolvers [Member]
Debt instruments, interest rate, effective percentage:
LIBOR		2.49%
Applicable margin interest rate		1.15%
Sum of LIBOR and margin, maximum rate		3.64%
Debt instruments, face, payment, and remaining balance amount:
Aggregate borrowing capacity, amount		$ 555,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date		May 31, 2024
Uhaul Intl and Subsidiaries [Member] | Capital Lease Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
New capital lease obligations, amount		$ 348,400
Capitalized assets, net book value		$ 1,574,000	$ 1,407,600
Uhaul Intl and Subsidiaries [Member] | Capital Lease Obligations [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage		1.92%
Uhaul Intl and Subsidiaries [Member] | Capital Lease Obligations [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage		5.04%
Amerco, Us Bank, National Association, Trustee [Member] | Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable		$ 85,600
Subsidiary holdings of parent company debt		$ 3,200
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start		Jan. 01, 2019
Debt instrument, maturity date range, end		Dec. 31, 2048
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%
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%
Life Insurance [Member] | FHLB [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Deposit amount	$ 60,000
Deposit earliest maturity date	Sep. 29, 2019
Deposit latest maturity date	Mar. 29, 2021
Available for sale equity securities, noncurrent	$ 124,400
Available for sale equity securities pledged as collateral	$ 69,800
Life Insurance [Member] | FHLB [Member] | Minimum [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Deposit interest rate	1.67%
Life Insurance [Member] | FHLB [Member] | Maximum [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Deposit interest rate	2.95%