Related Party Transactions (Table Text Block)	12 Months Ended
	Mar. 31, 2023
Related Party Revenue [Abstract]
Related Party Revenue	Years Ended March 31,     2023   2022   2021     (In thousands) U-Haul management fee revenue from Blackwater $ 29,825 $ 28,546 $ 25,512 U-Haul management fee revenue from Mercury   7,248   6,648   6,091  $ 37,073 $ 35,194 $ 31,603
Related Party Cost and Expense	Years Ended March 31,     2023   2022   2021     (In thousands) U-Haul lease expenses to Blackwater $ 2,416 $ 2,445 $ 2,612 U-Haul commission expenses to Blackwater   88,067   88,288   69,212  $ 90,483 $ 90,733 $ 71,824
Due from Related Party, Recap of Assets	March 31,     2023   2022     (In thousands) U-Haul receivable from Blackwater $ 42,141 $ 41,364 U-Haul receivable from Mercury   8,402   5,708 Other (a)   (2,235)   779  $ 48,308 $ 47,851