Borrowings (Narratives) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 3,975,764			$ 3,975,764		$ 3,513,076
Interest paid related to derivative contracts [Abstract]
Interest paid in cash	38,500		$ 32,700	109,600	$ 96,100
Real estate loan [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	105,413			105,413		135,287
Senior Mortgages [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	1,659,930			1,659,930		1,487,645
Working Capital Loans [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	335,000			335,000		55,000
Rental Truck (amortizing loans) First Loan [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	281,329			281,329		342,971
Capital Lease Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	1,012,791			1,012,791		984,217
Capital Lease Obligations [Member] | AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
New capital lease obligations, amount				255,300
Notes, loans and leases payable	1,012,800			1,012,800		984,200
Capitalized assets, net book value	$ 1,479,900			$ 1,479,900		1,407,600
Debt instruments, miscellaneous information:
Terms of lease				Between 5 and 7 years
Capital Lease Obligations [Member] | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.92%			1.92%
Capital Lease Obligations [Member] | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	5.04%			5.04%
Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 79,064			$ 79,064		$ 73,579
Amerco Real Estate Subsidiaries and Uhaul Company of Florida [Member] | Real estate loan [Member] | Uhaul International, Inc [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	2.39%			2.39%
Applicable margin interest rate	1.50%			1.50%
Sum of LIBOR and margin	3.89%			3.89%
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 105,400			$ 105,400
Debt instruments, issuance and maturity dates:
Mortgage loans on real estate, final maturity date				Apr. 30, 2023
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	$ 1,659,900			$ 1,659,900
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jan. 01, 2021
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	6.62%			6.62%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working Capital Loans [Member] | AMERCO [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	2.34%			2.34%
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 235,000			$ 235,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jun. 01, 2021
Debt instrument, maturity date range, end				Oct. 31, 2021
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working Capital Loans [Member] | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, effective percentage:
Applicable margin interest rate	1.25%			1.25%
Sum of LIBOR and margin	3.59%			3.59%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working Capital Loans [Member] | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, effective percentage:
Applicable margin interest rate	1.38%			1.38%
Sum of LIBOR and margin	3.72%			3.72%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working Capital Loans Two [Member] | AMERCO [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	2.32%			2.32%
Applicable margin interest rate	1.38%			1.38%
Sum of LIBOR and margin	3.70%			3.70%
Unused capacity fee				0.30%
Debt instruments, face, payment, and remaining balance amount:
Debt instrument, original face amount	$ 150,000			$ 150,000
Line of credit facility, maximum borrowing capacity	300,000			300,000
Notes, loans and leases payable	100,000			$ 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]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 281,300			$ 281,300
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Apr. 01, 2019
Debt instrument, maturity date range, end				Nov. 30, 2025
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	2.35%			2.35%
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	3.00%			3.00%
Debt instruments, interest rate, effective percentage:
LIBOR	2.46%			2.46%
Applicable margin interest rate	1.75%			1.75%
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	$ 258,600			$ 258,600
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	4.66%			4.66%
Uhaul Intl and Subsidiaries [Member] | Revolving fleet loans [Member]
Debt instruments, interest rate, effective percentage:
Applicable margin interest rate	1.15%			1.15%
Debt instruments, face, payment, and remaining balance amount:
Debt instrument, original face amount	$ 555,000			$ 555,000
Notes, loans and leases payable	$ 530,000			$ 530,000
Debt instruments, issuance and maturity dates:
Debt instrument, maturity date range, start				Jan. 01, 2021
Debt instrument, maturity date range, end				Apr. 30, 2023
Uhaul Intl and Subsidiaries [Member] | Revolving fleet loans [Member] | Minimum [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	2.34%			2.34%
Sum of LIBOR and margin	3.49%			3.49%
Uhaul Intl and Subsidiaries [Member] | Revolving fleet loans [Member] | Maximum [Member]
Debt instruments, interest rate, effective percentage:
LIBOR	2.35%			2.35%
Sum of LIBOR and margin	3.50%			3.50%
Amerco, Us Bank, National Association, Trustee [Member] | Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 82,300			$ 82,300
Subsidiary holdings of parent company debt	$ 3,300			$ 3,300
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%			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 activity for current period:
Aggregate deposit amount		$ 60,000
Available for sale investments, noncurrent		122,100
Available for sale equity securities pledged as collateral		$ 69,800
Life Insurance [Member] | Federal Home Loan Bank [Member] | Minimum [Member]
Federal home loan bank activity for current period:
Aggregate deposit amount fixed interest rate		1.67%
Aggregate deposit maturity date		Sep. 29, 2019
Life Insurance [Member] | Federal Home Loan Bank [Member] | Maximum [Member]
Federal home loan bank activity for current period:
Aggregate deposit amount fixed interest rate		2.95%
Aggregate deposit maturity date		Mar. 29, 2021