Related Party Transactions (Related Party Assets) (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Mar. 31, 2017
Related party assets:
U-Haul receivables		$ 4,284	$ 3,649
Related party assets		33,276	86,168
Blackwater [Member]
Related party assets:
Notes receivable			48,098
U-Haul interest receivable			5,397
U-Haul receivables		24,034	23,202
Mercury [Member]
Related party assets:
U-Haul receivables		10,357	9,195
Insurance Subsidiaries [Member]
Related party assets:
Other	[1]	$ (1,115)	$ 276

[1] Timing differences for intercompany balances with insurance subsidiaries resulting from the three month difference in reporting periods