Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2016		Mar. 31, 2015		Mar. 31, 2014
Revenues:
Self-moving equipment rentals		$ 2,297,980		$ 2,146,391		$ 1,955,423
Self-storage revenues		247,944		211,136		181,794
Self-moving and self-storage products and service sales		251,541		244,177		234,187
Property management fees		26,533		25,341		24,493
Life insurance premiums		162,662		156,103		157,919
Property and casualty insurance premiums		50,020		46,456		41,052
Net investment and interest income		86,805		84,728		79,591
Other revenue		152,171		160,199		160,793
Total revenues		3,275,656		3,074,531		2,835,252
Costs and expenses:
Operating expenses		1,470,047		1,479,409		1,313,674
Commission expenses		262,627		249,642		227,332
Cost of sales		144,990		146,072		127,270
Benefits and losses		167,436		158,760		156,702
Amortization of deferred policy acquisition costs		23,272		19,661		19,982
Lease expense		49,780		79,798		100,466
Depreciation, net of (gains) losses on disposals		290,690		278,165		259,612
Total costs and expenses		2,408,842		2,411,507		2,205,038
Earnings from operations before equity in earnings of subsidiaries		$ 866,814		$ 663,024		$ 630,214
Equity in earnings of subsidiaries
Earnings from operations		$ 866,814		$ 663,024		$ 630,214
Interest expense		$ (97,903)		(97,525)		$ (92,692)
Fees and amortization on early extinguishment of debt				(4,081)
Total pretax earnings		$ 768,911		561,418		$ 537,522
Income tax expense		(279,910)		(204,677)		(195,131)
Earnings available to common shareholders		489,001		356,741		342,391
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals		2,301,586		2,149,986		1,958,209
Self-storage revenues		247,944		211,136		181,794
Self-moving and self-storage products and service sales		251,541		244,177		234,187
Property management fees		$ 26,533		$ 25,341		$ 24,493
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income		$ 8,801		$ 13,644		$ 15,212
Other revenue		148,099		156,154		158,055
Total revenues		2,984,504		2,800,438		2,571,950
Costs and expenses:
Operating expenses		1,423,107		1,436,145		1,272,406
Commission expenses		262,627		249,642		227,332
Cost of sales		$ 144,990		$ 146,072		$ 127,270
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense		$ 49,966		$ 79,984		$ 100,649
Depreciation, net of (gains) losses on disposals		290,690		278,165		259,612
Total costs and expenses		2,171,380		2,190,008		1,987,269
Earnings from operations before equity in earnings of subsidiaries		813,124		610,430		584,681
Equity in earnings of subsidiaries		35,522		34,783		29,992
Earnings from operations		848,646		645,213		614,673
Interest expense		(98,533)		(98,163)		(93,162)
Fees and amortization on early extinguishment of debt				(4,081)
Total pretax earnings		750,113		542,969		521,511
Income tax expense		(261,112)		(186,228)		(179,120)
Earnings available to common shareholders		$ 489,001		$ 356,741		$ 342,391
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]		[3]
Self-storage revenues			[1]		[2]		[3]
Self-moving and self-storage products and service sales			[1]		[2]		[3]
Property management fees			[1]		[2]		[3]
Life insurance premiums			[1]		[2]		[3]
Property and casualty insurance premiums		$ 50,020	[1]	$ 46,456	[2]	$ 41,052	[3]
Net investment and interest income		$ 14,783	[1]	$ 12,819	[2]	$ 10,592	[3]
Other revenue			[1]		[2]		[3]
Total revenues		$ 64,803	[1]	$ 59,275	[2]	$ 51,644	[3]
Costs and expenses:
Operating expenses		$ 27,958	[1]	$ 24,802	[2]	$ 20,799	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		$ 12,298	[1]	$ 10,996	[2]	$ 11,513	[3]
Amortization of deferred policy acquisition costs			[1]		[2]		[3]
Lease expense			[1]		[2]		[3]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]
Total costs and expenses		$ 40,256	[1]	$ 35,798	[2]	$ 32,312	[3]
Earnings from operations before equity in earnings of subsidiaries		$ 24,547	[1]	$ 23,477	[2]	$ 19,332	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		$ 24,547	[1]	$ 23,477	[2]	$ 19,332	[3]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt	[2]
Total pretax earnings		$ 24,547	[1]	$ 23,477	[2]	$ 19,332	[3]
Income tax expense		(8,379)	[1]	(8,060)	[2]	(6,670)	[3]
Earnings available to common shareholders		$ 16,168	[1]	$ 15,417	[2]	$ 12,662	[3]
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]		[3]
Self-storage revenues			[1]		[2]		[3]
Self-moving and self-storage products and service sales			[1]		[2]		[3]
Property management fees			[1]		[2]		[3]
Life insurance premiums		$ 162,662	[1]	$ 156,103	[2]	$ 157,919	[3]
Property and casualty insurance premiums			[1]		[2]		[3]
Net investment and interest income		$ 63,999	[1]	$ 59,051	[2]	$ 54,398	[3]
Other revenue		4,559	[1]	4,502	[2]	3,211	[3]
Total revenues		231,220	[1]	219,656	[2]	215,528	[3]
Costs and expenses:
Operating expenses		$ 23,037	[1]	$ 22,476	[2]	$ 23,686	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		$ 155,138	[1]	$ 147,764	[2]	$ 145,189	[3]
Amortization of deferred policy acquisition costs		$ 23,272	[1]	$ 19,661	[2]	$ 19,982	[3]
Lease expense			[1]		[2]		[3]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]
Total costs and expenses		$ 201,447	[1]	$ 189,901	[2]	$ 188,857	[3]
Earnings from operations before equity in earnings of subsidiaries		$ 29,773	[1]	$ 29,755	[2]	$ 26,671	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		$ 29,773	[1]	$ 29,755	[2]	$ 26,671	[3]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt	[2]
Total pretax earnings		$ 29,773	[1]	$ 29,755	[2]	$ 26,671	[3]
Income tax expense		(10,419)	[1]	(10,389)	[2]	(9,341)	[3]
Earnings available to common shareholders		19,354	[1]	19,366	[2]	17,330	[3]
Eliminations [Member]
Revenues:
Self-moving equipment rentals	[4]	$ (3,606)		$ (3,595)		$ (2,786)
Self-storage revenues
Self-moving and self-storage products and service sales
Property management fees
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income	[5]	$ (778)		$ (786)		$ (611)
Other revenue	[5]	(487)		(457)		(473)
Total revenues		(4,871)		(4,838)		(3,870)
Costs and expenses:
Operating expenses	[4],[5]	$ (4,055)		$ (4,014)		$ (3,217)
Commission expenses
Cost of sales
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense	[5]	$ (186)		$ (186)		$ (183)
Depreciation, net of (gains) losses on disposals
Total costs and expenses		$ (4,241)		$ (4,200)		$ (3,400)
Earnings from operations before equity in earnings of subsidiaries		(630)		(638)		(470)
Equity in earnings of subsidiaries	[6]	(35,522)		(34,783)		(29,992)
Earnings from operations		(36,152)		(35,421)		(30,462)
Interest expense	[5]	630		$ 638		470
Fees and amortization on early extinguishment of debt
Total pretax earnings		$ (35,522)		$ (34,783)		$ (29,992)
Income tax expense
Earnings available to common shareholders		$ (35,522)		$ (34,783)		$ (29,992)

[1] Balances for the year ended December 31, 2015

[2] Balances for the year ended December 31, 2014

[3] Balances for the year ended December 31, 2013

[4] Eliminate intercompany premiums

[5] Eliminate intercompany lease / interest income

[6] Eliminate equity in earnings of subsidiaries