Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Revenues:
Self-moving equipment rentals	$ 3,877,917	$ 3,958,807	$ 3,083,317
Self-storage revenues	744,492	617,120	477,262
Self-moving and self-storage products and service sales	357,286	351,447	344,929
Property management fees	37,073	35,194	31,603
Life insurance premiums	99,149	111,027	121,609
Property and casualty insurance premiums	93,209	86,518	68,779
Net investment and interest income	176,679	148,261	122,938
Other revenue	478,886	431,373	291,548
Total revenues	5,864,691	5,739,747	4,541,985
Costs and expenses:
Operating expenses	3,024,547	2,676,541	2,187,684
Commission expenses	416,315	429,581	329,609
Cost of sales	263,026	259,585	214,059
Benefits and losses	165,553	186,647	179,512
Amortization of deferred policy acquisition costs	27,924	33,854	28,293
Lease expense	30,829	29,910	28,470
Depreciation, net of (gains) losses on disposals	486,795	482,752	609,930
Net gains on disposal of real estate	5,596	(4,120)	3,281
Total costs and expenses	4,420,585	4,094,750	3,580,838
Earnings from operations before equity in earnings of subsidiaries	1,444,106	1,644,997	961,147
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	1,444,106	1,644,997	961,147
Other components of net periodic benefit costs	(1,216)	(1,120)	(987)
Interest expense	(223,958)	(167,424)	(163,502)
Fees and amortization on early extinguishment of debt	(1,009)	(956)	0
Pretax earnings	1,217,923	1,475,497	796,658
Income tax expense	(294,925)	(352,211)	(185,802)
Earnings available to common shareholders	922,998	1,123,286	610,856
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	3,882,620	3,963,535	3,086,824
Self-storage revenues	744,492	617,120	477,262
Self-moving and self-storage products and service sales	357,286	351,447	344,929
Property management fees	37,073	35,194	31,603
Life insurance premiums	0	0	0
Property and casualty insurance premiums	0	0	0
Net investment and interest income	70,992	3,135	2,259
Other revenue	475,251	427,836	288,797
Total revenues	5,567,714	5,398,267	4,231,674
Costs and expenses:
Operating expenses	2,966,982	2,621,270	2,137,381
Commission expenses	416,315	429,581	329,609
Cost of sales	263,026	259,585	214,059
Benefits and losses	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	32,878	31,973	30,551
Depreciation, net of (gains) losses on disposals	486,795	482,752	609,930
Net gains on disposal of real estate	5,596	(4,120)	3,281
Total costs and expenses	4,171,592	3,821,041	3,324,811
Earnings from operations before equity in earnings of subsidiaries	1,396,122	1,577,226	906,863
Equity in earnings of subsidiaries	39,727	54,746	44,441
Earnings from operations	1,435,849	1,631,972	951,304
Other components of net periodic benefit costs	(1,216)	(1,120)	(987)
Interest expense	(224,999)	(168,491)	(164,592)
Fees and amortization on early extinguishment of debt	(1,009)	(956)
Pretax earnings	1,208,625	1,461,405	785,725
Income tax expense	(285,627)	(338,119)	(174,869)
Earnings available to common shareholders	922,998	1,123,286	610,856
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0
Self-storage revenues	0	0	0
Self-moving and self-storage products and service sales	0	0	0
Property management fees	0	0	0
Life insurance premiums	0	0	0
Property and casualty insurance premiums	96,242	89,667	70,285
Net investment and interest income	7,270	25,376	16,452
Other revenue	0	0	0
Total revenues	103,512	115,043	86,737
Costs and expenses:
Operating expenses	45,035	42,456	35,450
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	21,535	22,448	18,558
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	372	359	231
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	66,942	65,263	54,239
Earnings from operations before equity in earnings of subsidiaries	36,570	49,780	32,498
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	36,570	49,780	32,498
Other components of net periodic benefit costs	0	0	0
Interest expense	0	0	0
Fees and amortization on early extinguishment of debt	0	0
Pretax earnings	36,570	49,780	32,498
Income tax expense	(6,815)	(10,378)	(6,778)
Earnings available to common shareholders	29,755	39,402	25,720
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0
Self-storage revenues	0	0	0
Self-moving and self-storage products and service sales	0	0	0
Property management fees	0	0	0
Life insurance premiums	99,149	111,027	121,609
Property and casualty insurance premiums	0	0	0
Net investment and interest income	102,448	123,809	107,745
Other revenue	4,503	3,976	3,280
Total revenues	206,100	238,812	232,634
Costs and expenses:
Operating expenses	21,115	21,112	20,376
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	144,018	164,199	160,954
Amortization of deferred policy acquisition costs	27,924	33,854	28,293
Lease expense	108	109	135
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	193,165	219,274	209,758
Earnings from operations before equity in earnings of subsidiaries	12,935	19,538	22,876
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	12,935	19,538	22,876
Other components of net periodic benefit costs	0	0	0
Interest expense	(480)	(480)	0
Fees and amortization on early extinguishment of debt	0	0
Pretax earnings	12,455	19,058	22,876
Income tax expense	(2,483)	(3,714)	(4,155)
Earnings available to common shareholders	9,972	15,344	18,721
Eliminations [Member]
Revenues:
Self-moving equipment rentals	(4,703)	(4,728)	(3,507)
Self-storage revenues	0	0	0
Self-moving and self-storage products and service sales	0	0	0
Property management fees	0	0	0
Life insurance premiums	0	0	0
Property and casualty insurance premiums	(3,033)	(3,149)	(1,506)
Net investment and interest income	(4,031)	(4,059)	(3,518)
Other revenue	(868)	(439)	(529)
Total revenues	(12,635)	(12,375)	(9,060)
Costs and expenses:
Operating expenses	(8,585)	(8,297)	(5,523)
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	(2,529)	(2,531)	(2,447)
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	(11,114)	(10,828)	(7,970)
Earnings from operations before equity in earnings of subsidiaries	(1,521)	(1,547)	(1,090)
Equity in earnings of subsidiaries	(39,727)	(54,746)	(44,441)
Earnings from operations	(41,248)	(56,293)	(45,531)
Other components of net periodic benefit costs	0	0	0
Interest expense	1,521	1,547	1,090
Fees and amortization on early extinguishment of debt	0	0
Pretax earnings	(39,727)	(54,746)	(44,441)
Income tax expense	0	0	0
Earnings available to common shareholders	$ (39,727)	$ (54,746)	$ (44,441)