Related Party Transations (Table Text Block)	3 Months Ended	9 Months Ended
	Dec. 31, 2019	Dec. 31, 2019
Related Party Revenue [Abstract]
Related Party Revenue	Quarter Ended December 31,     2019   2018     (Unaudited)     (In thousands) U-Haul management fee revenue from Blackwater $ 5,763 $ 5,776 U-Haul management fee revenue from Mercury   3,335   2,123   $ 9,098 $ 7,899	Nine Months Ended December 31,     2019   2018     (Unaudited)     (In thousands) U-Haul management fee revenue from Blackwater $ 18,330 $ 18,254 U-Haul management fee revenue from Mercury   5,157   4,253   $ 23,487 $ 22,507
Related Party costs and expenses	Quarter Ended December 31,     2019   2018     (Unaudited)     (In thousands) U-Haul lease expenses to Blackwater $ 658 $ 669 U-Haul commission expenses to Blackwater   14,140   14,296   $ 14,798 $ 14,965	Nine Months Ended December 31,     2019   2018     (Unaudited)     (In thousands) U-Haul lease expenses to Blackwater $ 1,974 $ 2,009 U-Haul commission expenses to Blackwater   49,959   49,129   $ 51,933 $ 51,138
Related party assets		December 31,   March 31,     2019   2019     (Unaudited)         (In thousands) U-Haul receivable from Blackwater $ 37,840 $ 25,158 U-Haul receivable from Mercury   9,720   7,234 Other (a)   428   (1,503)   $ 47,988 $ 30,889 (a)       Timing differences for intercompany balances with insurance subsidiaries resulting from the three-month difference in reporting periods .