Schedule V - AMERCO and Consolidated Subsidiaries, Supplemental Information (for Property-Casualty Insurance Operations) (Details) - Amerco [Member] - Property Casualty Insurance Operations [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental information for property, casualty insurance underwriters:
Deferred policy acquisition costs
Reserves for unpaid claims and claims adjustment expense	233,554	244,400	251,964
Discount if any, deducted
Unearned premiums	70	49	59
Net earned premiums (1)	57,100	52,334	50,020
Net investment income (2)	14,079	14,015	13,491
Claim and claim adjustment expenses incurred related to current year	15,749	13,297	11,713
Claim and claim adjustment expenses incurred related to prior year	233	107	585
Amortization of deferred policy acquisition costs
Paid claims and claim adjustment expense	17,366	17,609	18,360
Net premiums written (1)	$ 57,123	$ 52,324	$ 50,034