Related Party Transactions (Related Party Assets) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Mar. 31, 2017
Related party assets:
Related party assets		$ 42,909	$ 86,168
Blackwater [Member]
Related party assets:
Notes receivable			48,098
U-Haul interest receivable			5,397
U-Haul receivables		31,915	23,203
Mercury [Member]
Related party assets:
U-Haul receivables		9,273	9,195
Insurance Group [Member]
Related party assets:
Other	[1]	$ 1,721	$ 276

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