Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands		Mar. 31, 2017		Dec. 31, 2016	Mar. 31, 2016		Dec. 31, 2015	Mar. 31, 2015		Mar. 31, 2014
ASSETS:
Cash and cash equivalents		$ 697,806			$ 600,646			$ 441,850		$ 495,112
Reinsurance recoverables and trade receivables, net		178,081			175,135
Inventories, net		82,439			79,756
Prepaid expenses		124,728			134,300
Investments, fixed maturities and marketable equities		1,663,768			1,490,789
Investments, other		367,830			311,821
Deferred policy acquisition costs, net		130,213			136,386
Other assets		117,072			77,210
Related party assets		86,168			85,734
Subtotal assets		3,448,105			3,091,777
Investments in subsidiaries
Property, plant and equipment, at cost:
Land		640,938			587,347
Buildings and improvements		2,606,537			2,187,400
Furniture and equipment		510,415			399,943
Property, plant and equipment (gross)		8,341,768			7,151,244
Less: Accumulated depreciation		(2,384,033)			(2,133,733)
Total property, plant and equipment		5,957,735			5,017,511
Total assets		9,405,840			8,109,288			6,855,600
Liabilities:
Accounts payable and accrued expenses		450,541			502,538
Notes, loans and leases payable		3,262,880			2,647,396
Policy benefits and losses, claims and loss expenses payable		1,086,322			1,071,412
Liabilities from investment contracts		1,112,498			951,490
Other policyholders' funds and liabilities		10,150			8,650
Deferred income		28,696			22,784
Deferred income taxes		835,009			653,612
Related party liabilities
Total liabilities		6,786,096			5,857,882
Stockholders' equity:
Additional paid-in capital		452,172			451,629
Accumulated other comprehensive loss		(51,236)			(60,525)
Retained earnings		2,892,893			2,533,641
Unearned employee stock ownership plan shares		(6,932)			(6,186)
Total stockholders' equity		2,619,744			2,251,406
Total liabilities and stockholders' equity		9,405,840			8,109,288
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		492,280			462,379
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		4,091,598			3,514,175
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		10,497			10,497
Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(525,663)			(525,653)
Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(151,997)			(151,997)
Operating Segments [Member] | Moving and Storage Consolidations [Member]
ASSETS:
Cash and cash equivalents		671,665			585,666			431,873		464,710
Reinsurance recoverables and trade receivables, net		41,234			34,451
Inventories, net		82,439			79,756
Prepaid expenses		124,728			134,300
Investments, fixed maturities and marketable equities
Investments, other		35,342			21,431
Deferred policy acquisition costs, net
Other assets		112,744			71,719
Related party assets		88,829			88,022
Subtotal assets		1,156,981			1,015,345
Investments in subsidiaries		477,058			432,277
Property, plant and equipment, at cost:
Land		640,938			587,347
Buildings and improvements		2,606,537			2,187,400
Furniture and equipment		510,415			399,943
Property, plant and equipment (gross)		8,341,768			7,151,244
Less: Accumulated depreciation		(2,384,033)			(2,133,733)
Total property, plant and equipment		5,957,735			5,017,511
Total assets		7,591,774			6,465,133
Liabilities:
Accounts payable and accrued expenses		441,667			492,907
Notes, loans and leases payable		3,262,880			2,647,396
Policy benefits and losses, claims and loss expenses payable		399,181			386,366
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income		28,696			22,784
Deferred income taxes		809,566			633,061
Related party liabilities		30,040			31,213
Total liabilities		4,972,030			4,213,727
Stockholders' equity:
Additional paid-in capital		452,382			451,839
Accumulated other comprehensive loss		(51,236)			(60,525)
Retained earnings		2,892,683			2,533,431
Unearned employee stock ownership plan shares		(6,932)			(6,186)
Total stockholders' equity		2,619,744			2,251,406
Total liabilities and stockholders' equity		7,591,774			6,465,133
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		492,280			462,379
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross		4,091,598			3,514,175
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		10,497			10,497
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(525,653)			(525,653)
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value		(151,997)			(151,997)
Operating Segments [Member] | Property and Casualty Insurance [Member]
ASSETS:
Cash and cash equivalents		12,725	[1]		14,049	[2]		8,495	[3]	12,758	[3]
Reinsurance recoverables and trade receivables, net		107,757	[1]		111,978	[2]
Inventories, net			[1]			[2]
Prepaid expenses			[1]			[2]
Investments, fixed maturities and marketable equities		248,816	[1]		238,570	[2]
Investments, other		63,086	[1]		47,374	[2]
Deferred policy acquisition costs, net			[1]			[2]
Other assets		1,922	[1]		3,088	[2]
Related party assets		11,496	[1]		12,465	[2]
Subtotal assets		445,802	[1]		427,524	[2]
Investments in subsidiaries			[1]			[2]
Property, plant and equipment, at cost:
Land			[1]			[2]
Buildings and improvements			[1]			[2]
Furniture and equipment			[1]			[2]
Property, plant and equipment (gross)			[1]			[2]
Less: Accumulated depreciation			[1]			[2]
Total property, plant and equipment			[1]			[2]
Total assets		445,802	[1]		427,524	[2]
Liabilities:
Accounts payable and accrued expenses		1,926	[1]		1,535	[2]
Notes, loans and leases payable			[1]			[2]
Policy benefits and losses, claims and loss expenses payable		244,980	[1]	$ 244,980	252,819	[2]	$ 252,819
Liabilities from investment contracts			[1]			[2]
Other policyholders' funds and liabilities		4,184	[1]		3,017	[2]
Deferred income			[1]			[2]
Deferred income taxes		11,243	[1]		7,526	[2]
Related party liabilities		2,539	[1]		2,067	[2]
Total liabilities		264,872	[1]		266,964	[2]
Stockholders' equity:
Additional paid-in capital		91,120	[1]		91,120	[2]
Accumulated other comprehensive loss		6,166	[1]		3,611	[2]
Retained earnings		80,343	[1]		62,528	[2]
Unearned employee stock ownership plan shares			[1]			[2]
Total stockholders' equity		180,930	[1]		160,560	[2]
Total liabilities and stockholders' equity		445,802	[1]		427,524	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		3,301	[1]		3,301	[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Property and Casualty Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Life Insurance [Member]
ASSETS:
Cash and cash equivalents		13,416	[1]		931	[2]		$ 1,482	[3]	$ 17,644	[3]
Reinsurance recoverables and trade receivables, net		29,090	[1]		28,706	[2]
Inventories, net			[1]			[2]
Prepaid expenses			[1]			[2]
Investments, fixed maturities and marketable equities		1,414,952	[1]		1,252,219	[2]
Investments, other		269,402	[1]		243,016	[2]
Deferred policy acquisition costs, net		130,213	[1]		136,386	[2]
Other assets		2,406	[1]		2,403	[2]
Related party assets		18,465	[1]		18,688	[2]
Subtotal assets		1,877,944	[1]		1,682,349	[2]
Investments in subsidiaries			[1]			[2]
Property, plant and equipment, at cost:
Land			[1]			[2]
Buildings and improvements			[1]			[2]
Furniture and equipment			[1]			[2]
Property, plant and equipment (gross)			[1]			[2]
Less: Accumulated depreciation			[1]			[2]
Total property, plant and equipment			[1]			[2]
Total assets		1,877,944	[1]		1,682,349	[2]
Liabilities:
Accounts payable and accrued expenses		6,948	[1]		8,096	[2]
Notes, loans and leases payable			[1]			[2]
Policy benefits and losses, claims and loss expenses payable		442,161	[1]		432,227	[2]
Liabilities from investment contracts		1,112,498	[1]		951,490	[2]
Other policyholders' funds and liabilities		5,966	[1]		5,633	[2]
Deferred income			[1]			[2]
Deferred income taxes		14,200	[1]		13,025	[2]
Related party liabilities		43	[1]		161	[2]
Total liabilities		1,581,816	[1]		1,410,632	[2]
Stockholders' equity:
Additional paid-in capital		26,271	[1]		26,271	[2]
Accumulated other comprehensive loss		16,933	[1]		10,504	[2]
Retained earnings		250,424	[1]		232,442	[2]
Unearned employee stock ownership plan shares			[1]			[2]
Total stockholders' equity		296,128	[1]		271,717	[2]
Total liabilities and stockholders' equity		1,877,944	[1]		1,682,349	[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued		2,500	[1]		2,500	[2]
Operating Segments [Member] | Life Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Operating Segments [Member] | Life Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value			[1]			[2]
Eliminations [Member]
ASSETS:
Cash and cash equivalents
Reinsurance recoverables and trade receivables, net
Inventories, net
Prepaid expenses
Investments, fixed maturities and marketable equities
Investments, other
Deferred policy acquisition costs, net
Other assets
Related party assets	[4]	(32,622)			(33,441)
Subtotal assets		(32,622)			(33,441)
Investments in subsidiaries	[5]	(477,058)			(432,277)
Property, plant and equipment, at cost:
Land
Buildings and improvements
Furniture and equipment
Property, plant and equipment (gross)
Less: Accumulated depreciation
Total property, plant and equipment
Total assets		(509,680)			(465,718)
Liabilities:
Accounts payable and accrued expenses
Notes, loans and leases payable
Policy benefits and losses, claims and loss expenses payable
Liabilities from investment contracts
Other policyholders' funds and liabilities
Deferred income
Deferred income taxes
Related party liabilities	[4]	(32,622)			(33,441)
Total liabilities		(32,622)			(33,441)
Stockholders' equity:
Additional paid-in capital	[5]	(117,601)			(117,601)
Accumulated other comprehensive loss	[5]	(23,099)			(14,115)
Retained earnings	[5]	(330,557)			(294,760)
Unearned employee stock ownership plan shares
Total stockholders' equity		(477,058)			(432,277)
Total liabilities and stockholders' equity		(509,680)			(465,718)
Eliminations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross
Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued
Eliminations [Member] | Series A Common Stock [Member]
Stockholders' equity:
Common stock, value, issued
Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	[5]	(5,801)			(5,801)
Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value
Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value

[1] Balances as of December 31, 2016

[2] Balances as of December 31, 2015

[3] Balance for the period ended December 31, 2014

[4] Eliminate intercompany receivables and payables

[5] Eliminate investment in subsidiaries