Related Party Transations (Table Text Block)	3 Months Ended	9 Months Ended
	Dec. 31, 2020	Dec. 31, 2020
Related Party Revenue [Abstract]
Related Party Revenue	Quarter Ended December 31,     2020   2019     (Unaudited)     (In thousands) U-Haul management fee revenue from Blackwater $ 6,350 $ 5,763 U-Haul management fee revenue from Mercury   2,415   3,335   $ 8,765 $ 9,098	Nine Months Ended December 31,     2020   2019     (Unaudited)     (In thousands) U-Haul management fee revenue from Blackwater $ 19,142 $ 18,330 U-Haul management fee revenue from Mercury   4,810   5,157   $ 23,952 $ 23,487
Related Party costs and expenses	Quarter Ended December 31,     2020   2019     (Unaudited)     (In thousands) U-Haul lease expenses to Blackwater $ 658 $ 658 U-Haul commission expenses to Blackwater   18,099   14,140   $ 18,757 $ 14,798	Nine Months Ended December 31,     2020   2019     (Unaudited)     (In thousands) U-Haul lease expenses to Blackwater $ 1,973 $ 1,974 U-Haul commission expenses to Blackwater   53,964   49,959   $ 55,937 $ 51,933
Related party assets		December 31,   March 31,     2020   2020     (Unaudited)         (In thousands) U-Haul receivable from Blackwater $ 36,171 $ 25,293 U-Haul receivable from Mercury   9,765   9,893 Other (a)   (10,973)   (402)   $ 34,963 $ 34,784 (a)       Timing differences for intercompany balances with insurance subsidiaries resulting from the three-month difference in reporting periods . Our credit balance as of December 31, 2020, was due to a net timing difference for a dividend paid by Repwest to AMERCO of $ 22.6 million and a surplus note entered into by Oxford with AMERCO for $ 12.0 million.