Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2017		Mar. 31, 2016		Mar. 31, 2015
Revenues:
Self-moving equipment rentals		$ 2,362,833		$ 2,297,980		$ 2,146,391
Self-storage revenues		286,886		247,944		211,136
Self-moving and self-storage products and service sales		253,073		251,541		244,177
Property management fees		29,075		26,533		25,341
Life insurance premiums		163,579		162,662		156,103
Property and casualty insurance premiums		52,334		50,020		46,456
Net investment and interest income		102,276		86,617		84,728
Other revenue		171,711		152,171		160,199
Total revenues		3,421,767		3,275,468		3,074,531
Costs and expenses:
Operating expenses		1,568,083		1,470,047		1,479,409
Commission expenses		267,230		262,627		249,642
Cost of sales		152,485		144,990		146,072
Benefits and losses		182,710		167,436		158,760
Amortization of deferred policy acquisition costs		26,218		23,272		19,661
Lease expense		37,343		49,780		79,798
Depreciation, net of (gains) losses on disposals		445,435		290,690		278,165
Total costs and expenses		2,679,504		2,408,842		2,411,507
Earnings from operations before equity in earnings of subsidiaries		742,263		866,626		663,024
Equity in earnings of subsidiaries
Earnings from operations		742,263		866,626		663,024
Interest expense		(113,406)		(97,715)		(97,525)
Fees and amortization on early extinguishment of debt		(499)				(4,081)
Pretax earnings		628,358		768,911		561,418
Income tax expense		(229,934)		(279,910)		(204,677)
Earnings available to common shareholders		398,424		489,001		356,741
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals		2,366,526		2,301,586		2,149,986
Self-storage revenues		286,886		247,944		211,136
Self-moving and self-storage products and service sales		253,073		251,541		244,177
Property management fees		29,075		26,533		25,341
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income		9,688		8,801		13,644
Other revenue		167,752		148,099		156,154
Total revenues		3,113,000		2,984,504		2,800,438
Costs and expenses:
Operating expenses		1,521,408		1,423,107		1,436,145
Commission expenses		267,230		262,627		249,642
Cost of sales		152,485		144,990		146,072
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense		37,529		49,966		79,984
Depreciation, net of (gains) losses on disposals		445,435		290,690		278,165
Total costs and expenses		2,424,087		2,171,380		2,190,008
Earnings from operations before equity in earnings of subsidiaries		688,913		813,124		610,430
Equity in earnings of subsidiaries		35,797		35,522		34,783
Earnings from operations		724,710		848,646		645,213
Interest expense		(114,863)		(98,533)		(98,163)
Fees and amortization on early extinguishment of debt		(499)				(4,081)
Pretax earnings		609,348		750,113		542,969
Income tax expense		(210,924)		(261,112)		(186,228)
Earnings available to common shareholders		398,424		489,001		356,741
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		52,334	[1]	50,020	[2]	46,456	[3]
Net investment and interest income		16,652	[1]	14,783	[2]	12,819	[3]
Other revenue			[1]		[2]		[3]
Total revenues		68,986	[1]	64,803	[2]	59,275	[3]
Costs and expenses:
Operating expenses		28,421	[1]	27,958	[2]	24,802	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		13,404	[1]	12,298	[2]	10,996	[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		41,825	[1]	40,256	[2]	35,798	[3]
Earnings from operations before equity in earnings of subsidiaries		27,161	[1]	24,547	[2]	23,477	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		27,161	[1]	24,547	[2]	23,477	[3]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt
Pretax earnings		27,161	[1]	24,547	[2]	23,477	[3]
Income tax expense		(9,346)	[1]	(8,379)	[2]	(8,060)	[3]
Earnings available to common shareholders		17,815	[1]	16,168	[2]	15,417	[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		163,579	[1]	162,662	[2]	156,103	[3]
Property and casualty insurance premiums			[1]		[2]		[3]
Net investment and interest income		77,540	[1]	63,999	[2]	59,051	[3]
Other revenue		4,480	[1]	4,559	[2]	4,502	[3]
Total revenues		245,599	[1]	231,220	[2]	219,656	[3]
Costs and expenses:
Operating expenses		22,429	[1]	23,037	[2]	22,476	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		169,306	[1]	155,138	[2]	147,764	[3]
Amortization of deferred policy acquisition costs		26,218	[1]	23,272	[2]	19,661	[3]
Lease expense			[1]		[2]		[3]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]
Total costs and expenses		217,953	[1]	201,447	[2]	189,901	[3]
Earnings from operations before equity in earnings of subsidiaries		27,646	[1]	29,773	[2]	29,755	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		27,646	[1]	29,773	[2]	29,755	[3]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt
Pretax earnings		27,646	[1]	29,773	[2]	29,755	[3]
Income tax expense		(9,664)	[1]	(10,419)	[2]	(10,389)	[3]
Earnings available to common shareholders		17,982	[1]	19,354	[2]	19,366	[3]
Eliminations [Member]
Revenues:
Self-moving equipment rentals	[4]	(3,693)		(3,606)		(3,595)
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]	(1,604)		(966)		(786)
Other revenue	[5]	(521)		(487)		(457)
Total revenues		(5,818)		(5,059)		(4,838)
Costs and expenses:
Operating expenses	[4],[5]	(4,175)		(4,055)		(4,014)
Commission expenses
Cost of sales
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense	[5]	(186)		(186)		(186)
Depreciation, net of (gains) losses on disposals
Total costs and expenses		(4,361)		(4,241)		(4,200)
Earnings from operations before equity in earnings of subsidiaries		(1,457)		(818)		(638)
Equity in earnings of subsidiaries	[6]	(35,797)		(35,522)		(34,783)
Earnings from operations		(37,254)		(36,340)		(35,421)
Interest expense	[5]	1,457		818		638
Fees and amortization on early extinguishment of debt
Pretax earnings		(35,797)		(35,522)		(34,783)
Income tax expense
Earnings available to common shareholders		$ (35,797)		$ (35,522)		$ (34,783)

[1] Balances for the year ended December 31, 2016

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

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

[4] Eliminate intercompany premiums

[5] Eliminate intercompany lease / interest income

[6] Eliminate equity in earnings of subsidiaries