Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Mar. 31, 2017
Revenues:
Self-moving equipment rentals		$ 2,653,497		$ 2,479,742		$ 2,362,833
Self-storage revenues		367,276		323,903		286,886
Self-moving and self-storage products and service sales		264,146		261,557		253,073
Property management fees		29,148		29,602		29,075
Life insurance premiums		63,488		154,703		163,579
Property and casualty insurance premiums		60,853		57,100		52,334
Net investment and interest income		110,934		110,473		102,276
Other revenue		219,365		184,034		171,711
Total revenues		3,768,707		3,601,114		3,421,767
Costs and expenses:
Operating expenses		1,981,180		1,807,056		1,567,181
Commission expenses		288,408		276,705		267,230
Cost of sales		162,142		160,489		152,485
Benefits and losses		100,277		185,311		182,710
Amortization of deferred policy acquisition costs		28,556		24,514		26,218
Lease expense		33,158		33,960		37,343
Depreciation, net of (gains) losses on disposals		554,043		543,247		449,025
Net gains on disposal of real estate		(44)		(195,414)		(3,590)
Total costs and expenses		3,147,720		2,835,868		2,678,602
Earnings from operations before equity in earnings of subsidiaries		620,987		765,246		743,165
Equity in earnings of subsidiaries
Earnings from operations		620,987		765,246		743,165
Other components of net periodic benefit costs		(1,013)		(927)		(902)
Interest expense		(142,445)		(126,706)		(113,406)
Fees and amortization on early extinguishment of debt						(499)
Pretax earnings		477,529		637,613		628,358
Income tax expense		(106,672)		152,970		(229,934)
Earnings available to common shareholders		370,857		790,583		398,424
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals		2,656,327		2,483,956		2,366,526
Self-storage revenues		367,276		323,903		286,886
Self-moving and self-storage products and service sales		264,146		261,557		253,073
Property management fees		29,148		29,602		29,075
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income		13,857		12,232		9,688
Other revenue		215,055		179,417		167,752
Total revenues		3,545,809		3,290,667		3,113,000
Costs and expenses:
Operating expenses		1,938,317		1,758,697		1,520,506
Commission expenses		288,408		276,705		267,230
Cost of sales		162,142		160,489		152,485
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense		33,702		34,243		37,529
Depreciation, net of (gains) losses on disposals		554,043		543,247		449,025
Net gains on disposal of real estate		(44)		(195,414)		(3,590)
Total costs and expenses		2,976,568		2,577,967		2,423,185
Earnings from operations before equity in earnings of subsidiaries		569,241		712,700		689,815
Equity in earnings of subsidiaries		41,811		46,990		35,797
Earnings from operations		611,052		759,690		725,612
Other components of net periodic benefit costs		(1,013)		(927)		(902)
Interest expense		(143,586)		(127,997)		(114,863)
Fees and amortization on early extinguishment of debt						(499)
Pretax earnings		466,453		630,766		609,348
Income tax expense		(95,596)		159,817		(210,924)
Earnings available to common shareholders		370,857		790,583		398,424
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		63,488	[1]	58,800	[2]	52,334	[3]
Net investment and interest income		12,349	[1]	15,771	[2]	16,652	[3]
Other revenue			[1]		[2]		[3]
Total revenues		75,837	[1]	74,571	[2]	68,986	[3]
Costs and expenses:
Operating expenses		34,218	[1]	32,710	[2]	28,421	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		14,213	[1]	15,983	[2]	13,404	[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]
Net gains on disposal of real estate			[1]		[2]		[3]
Total costs and expenses		48,431	[1]	48,693	[2]	41,825	[3]
Earnings from operations before equity in earnings of subsidiaries		27,406	[1]	25,878	[2]	27,161	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		27,406	[1]	25,878	[2]	27,161	[3]
Other components of net periodic benefit costs			[1]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt	[3]
Pretax earnings		27,406	[1]	25,878	[2]	27,161	[3]
Income tax expense		(5,698)	[1]	(2,989)	[2]	(9,346)	[3]
Earnings available to common shareholders		21,708	[1]	22,889	[2]	17,815	[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		63,488	[1]	154,703	[2]	163,579	[3]
Property and casualty insurance premiums			[1]		[2]		[3]
Net investment and interest income		86,395	[1]	84,158	[2]	77,540	[3]
Other revenue		4,831	[1]	5,001	[2]	4,480	[3]
Total revenues		154,714	[1]	243,862	[2]	245,599	[3]
Costs and expenses:
Operating expenses		14,613	[1]	22,061	[2]	22,429	[3]
Commission expenses			[1]		[2]		[3]
Cost of sales			[1]		[2]		[3]
Benefits and losses		86,064	[1]	169,328	[2]	169,306	[3]
Amortization of deferred policy acquisition costs		28,556	[1]	24,514	[2]	26,218	[3]
Lease expense			[1]		[2]		[3]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]
Net gains on disposal of real estate			[1]		[2]		[3]
Total costs and expenses		129,233	[1]	215,903	[2]	217,953	[3]
Earnings from operations before equity in earnings of subsidiaries		25,481	[1]	27,959	[2]	27,646	[3]
Equity in earnings of subsidiaries			[1]		[2]		[3]
Earnings from operations		25,481	[1]	27,959	[2]	27,646	[3]
Other components of net periodic benefit costs			[1]
Interest expense			[1]		[2]		[3]
Fees and amortization on early extinguishment of debt	[3]
Pretax earnings		25,481	[1]	27,959	[2]	27,646	[3]
Income tax expense		(5,378)	[1]	(3,858)	[2]	(9,664)	[3]
Earnings available to common shareholders		20,103	[1]	24,101	[2]	17,982	[3]
Eliminations [Member]
Revenues:
Self-moving equipment rentals	[4]	(2,830)		(4,214)		(3,693)
Self-storage revenues
Self-moving and self-storage products and service sales
Property management fees
Life insurance premiums
Property and casualty insurance premiums		(2,635)		(1,700)
Net investment and interest income	[5]	(1,667)		(1,688)		(1,604)
Other revenue	[5]	(521)		(384)		(521)
Total revenues		(7,653)		(7,986)		(5,818)
Costs and expenses:
Operating expenses	[4],[5]	(5,968)		(6,412)		(4,175)
Commission expenses
Cost of sales
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense	[5]	(544)		(283)		(186)
Depreciation, net of (gains) losses on disposals
Net gains on disposal of real estate
Total costs and expenses		(6,512)		(6,695)		(4,361)
Earnings from operations before equity in earnings of subsidiaries		(1,141)		(1,291)		(1,457)
Equity in earnings of subsidiaries	[6]	(41,811)		(46,990)		(35,797)
Earnings from operations		(42,952)		(48,281)		(37,254)
Other components of net periodic benefit costs
Interest expense	[5]	1,141		1,291		1,457
Fees and amortization on early extinguishment of debt
Pretax earnings		(41,811)		(46,990)		(35,797)
Income tax expense
Earnings available to common shareholders		$ (41,811)		$ (46,990)		$ (35,797)

[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