Schedule V - AMERCO and Consolidated Subsidiaries, Supplemental Information (for Property-Casualty Insurance Operations), Parenthetical (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net investment income excludes net realized (gains) losses on investments:
Earned premiums eliminated	[1]	$ 211,803	$ 215,913	$ 212,682
Amerco [Member] | Property Casualty Insurance Operations [Member]
Net investment income excludes net realized (gains) losses on investments:
Earned premiums eliminated		0	0	0
Investment Income		$ (1,700)	$ (2,600)	$ (1,300)

[1] Balances are reported net of inter-segment transactions