Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Self-moving equipment rentals	$ 3,083,317	$ 2,692,413	$ 2,653,497
Self-storage revenues	477,262	418,741	367,276
Self-moving and self-storage products and service sales	344,929	265,091	264,146
Property management fees	31,603	30,406	29,148
Life insurance premiums	121,609	127,976	63,488
Property and casualty insurance premiums	68,779	66,053	60,853
Net investment and interest income	122,938	137,829	110,934
Other revenue	291,548	240,359	219,365
Total revenues	4,541,985	3,978,868	3,768,707
Costs and expenses:
Operating expenses	2,187,684	2,117,148	1,981,180
Commission expenses	329,609	288,332	288,408
Cost of sales	214,059	164,018	162,142
Benefits and losses	179,512	174,836	100,277
Amortization of deferred policy acquisition costs	28,293	31,219	28,556
Lease expense	28,470	26,882	33,158
Depreciation, net of (gains) losses on disposals	609,930	637,063	554,043
Net gains on disposal of real estate	3,281	(758)	(44)
Total costs and expenses	3,580,838	3,438,740	3,147,720
Earnings from operations before equity in earnings of subsidiaries	961,147	540,128	620,987
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	961,147	540,128	620,987
Other components of net periodic benefit costs	(987)	(1,054)	(1,013)
Interest expense	(163,502)	(160,950)	(142,445)
Pretax earnings	796,658	378,124	477,529
Income tax expense	(185,802)	63,924	(106,672)
Earnings available to common shareholders	610,856	442,048	370,857
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	3,086,824	2,696,516	2,656,327
Self-storage revenues	477,262	418,741	367,276
Self-moving and self-storage products and service sales	344,929	265,091	264,146
Property management fees	31,603	30,406	29,148
Life insurance premiums	0	0	0
Property and casualty insurance premiums	0	0	0
Net investment and interest income	2,259	10,593	13,857
Other revenue	288,797	236,419	215,055
Total revenues	4,231,674	3,657,766	3,545,809
Costs and expenses:
Operating expenses	2,137,381	2,069,655	1,938,317
Commission expenses	329,609	288,332	288,408
Cost of sales	214,059	164,018	162,142
Benefits and losses	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	30,551	27,494	33,702
Depreciation, net of (gains) losses on disposals	609,930	637,063	554,043
Net gains on disposal of real estate	3,281	(758)	(44)
Total costs and expenses	3,324,811	3,185,804	2,976,568
Earnings from operations before equity in earnings of subsidiaries	906,863	471,962	569,241
Equity in earnings of subsidiaries	44,441	55,789	41,811
Earnings from operations	951,304	527,751	611,052
Other components of net periodic benefit costs	(987)	(1,054)	(1,013)
Interest expense	(164,592)	(162,062)	(143,586)
Pretax earnings	785,725	364,635	466,453
Income tax expense	(174,869)	77,413	(95,596)
Earnings available to common shareholders	610,856	442,048	370,857
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	70,285	69,141	63,488
Net investment and interest income	16,452	19,923	12,349
Other revenue	0	0	0
Total revenues	86,737	89,064	75,837
Costs and expenses:
Operating expenses	35,450	33,770	34,218
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	18,558	12,410	14,213
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	231	0	0
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	54,239	46,180	48,431
Earnings from operations before equity in earnings of subsidiaries	32,498	42,884	27,406
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	32,498	42,884	27,406
Other components of net periodic benefit costs	0	0	0
Interest expense	0	0	0
Pretax earnings	32,498	42,884	27,406
Income tax expense	(6,778)	(8,956)	(5,698)
Earnings available to common shareholders	25,720	33,928	21,708
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	121,609	127,976	63,488
Property and casualty insurance premiums	0	0	0
Net investment and interest income	107,745	109,018	86,395
Other revenue	3,280	4,470	4,831
Total revenues	232,634	241,464	154,714
Costs and expenses:
Operating expenses	20,376	21,425	14,613
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	160,954	162,426	86,064
Amortization of deferred policy acquisition costs	28,293	31,219	28,556
Lease expense	135	0	0
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	209,758	215,070	129,233
Earnings from operations before equity in earnings of subsidiaries	22,876	26,394	25,481
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	22,876	26,394	25,481
Other components of net periodic benefit costs	0	0	0
Interest expense	0	0	0
Pretax earnings	22,876	26,394	25,481
Income tax expense	(4,155)	(4,533)	(5,378)
Earnings available to common shareholders	18,721	21,861	20,103
Eliminations [Member]
Revenues:
Self-moving equipment rentals	(3,507)	(4,103)	(2,830)
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	(1,506)	(3,088)	(2,635)
Net investment and interest income	(3,518)	(1,705)	(1,667)
Other revenue	(529)	(530)	(521)
Total revenues	(9,060)	(9,426)	(7,653)
Costs and expenses:
Operating expenses	(5,523)	(7,702)	(5,968)
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	(2,447)	(612)	(544)
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	(7,970)	(8,314)	(6,512)
Earnings from operations before equity in earnings of subsidiaries	(1,090)	(1,112)	(1,141)
Equity in earnings of subsidiaries	(44,441)	(55,789)	(41,811)
Earnings from operations	(45,531)	(56,901)	(42,952)
Other components of net periodic benefit costs	0	0	0
Interest expense	1,090	1,112	1,141
Pretax earnings	(44,441)	(55,789)	(41,811)
Income tax expense	0	0	0
Earnings available to common shareholders	$ (44,441)	$ (55,789)	$ (41,811)