Related Party Transactions (Table Text Block)	12 Months Ended
	Mar. 31, 2022
Related Party Revenue [Abstract]
Related Party Revenue	Years Ended March 31,     2022   2021   2020     (In thousands) U-Haul management fee revenue from Blackwater $ 28,546 $ 25,512 $ 24,014 U-Haul management fee revenue from Mercury   6,648   6,091   6,392  $ 35,194 $ 31,603 $ 30,406
Related Party Cost and Expense	Years Ended March 31,     2022   2021   2020     (In thousands) U-Haul lease expenses to Blackwater $ 2,445 $ 2,612 $ 2,631 U-Haul commission expenses to Blackwater   88,288   69,212   62,066  $ 90,733 $ 71,824 $ 64,697
Due from Related Party, Recap of Assets	March 31,     2022   2021     (In thousands) U-Haul receivable from Blackwater $ 41,364 $ 27,116 U-Haul receivable from Mercury   5,708   9,632 Other (a)   779   (1,353)  $ 47,851 $ 35,395