Consolidating financial information by industry segment (Statement of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Self-moving equipment rentals	$ 2,692,413	$ 2,653,497	$ 2,479,742
Self-storage revenues	418,741	367,276	323,903
Self-moving and self-storage products and service sales	265,091	264,146	261,557
Property management fees	30,406	29,148	29,602
Life insurance premiums	127,976	63,488	154,703
Property and casualty insurance premiums	66,053	60,853	57,100
Net investment and interest income	137,829	110,934	110,473
Other revenue	240,359	219,365	184,034
Total revenues	3,978,868	3,768,707	3,601,114
Costs and expenses:
Operating expenses	2,117,148	1,981,180	1,807,056
Commission expenses	288,332	288,408	276,705
Cost of sales	164,018	162,142	160,489
Benefits and losses	174,836	100,277	185,311
Amortization of deferred policy acquisition costs	31,219	28,556	24,514
Lease expense	26,882	33,158	33,960
Depreciation, net of (gains) losses on disposals	637,063	554,043	543,247
Net gains on disposal of real estate	(758)	(44)	(195,414)
Total costs and expenses	3,438,740	3,147,720	2,835,868
Earnings from operations before equity in earnings of subsidiaries	540,128	620,987	765,246
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	540,128	620,987	765,246
Pretax earnings	378,124	477,529	637,613
Earnings available to common shareholders	442,048	370,857	790,583
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	2,696,516	2,656,327	2,483,956
Self-storage revenues	418,741	367,276	323,903
Self-moving and self-storage products and service sales	265,091	264,146	261,557
Property management fees	30,406	29,148	29,602
Life insurance premiums	0	0	0
Property and casualty insurance premiums	0	0	0
Net investment and interest income	10,593	13,857	12,232
Other revenue	236,419	215,055	179,417
Total revenues	3,657,766	3,545,809	3,290,667
Costs and expenses:
Operating expenses	2,069,655	1,938,317	1,758,697
Commission expenses	288,332	288,408	276,705
Cost of sales	164,018	162,142	160,489
Benefits and losses	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	27,494	33,702	34,243
Depreciation, net of (gains) losses on disposals	637,063	554,043	543,247
Net gains on disposal of real estate	(758)	(44)	(195,414)
Total costs and expenses	3,185,804	2,976,568	2,577,967
Earnings from operations before equity in earnings of subsidiaries	471,962	569,241	712,700
Equity in earnings of subsidiaries	55,789	41,811	46,990
Earnings from operations	527,751	611,052	759,690
Other components of net periodic benefit costs	(1,054)	(1,013)	(927)
Interest expense	(162,062)	(143,586)	(127,997)
Pretax earnings	364,635	466,453	630,766
Income tax expense	77,413	(95,596)	159,817
Earnings available to common shareholders	442,048	370,857	790,583
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	69,141	63,488	58,800
Net investment and interest income	19,923	12,349	15,771
Other revenue	0	0	0
Total revenues	89,064	75,837	74,571
Costs and expenses:
Operating expenses	33,770	34,218	32,710
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	12,410	14,213	15,983
Amortization of deferred policy acquisition costs	0	0	0
Lease expense	0	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	46,180	48,431	48,693
Earnings from operations before equity in earnings of subsidiaries	42,884	27,406	25,878
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	42,884	27,406	25,878
Other components of net periodic benefit costs	0	0	0
Interest expense	0	0	0
Pretax earnings	42,884	27,406	25,878
Income tax expense	(8,956)	(5,698)	(2,989)
Earnings available to common shareholders	33,928	21,708	22,889
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	127,976	63,488	154,703
Property and casualty insurance premiums	0	0	0
Net investment and interest income	109,018	86,395	84,158
Other revenue	4,470	4,831	5,001
Total revenues	241,464	154,714	243,862
Costs and expenses:
Operating expenses	21,425	14,613	22,061
Commission expenses	0	0	0
Cost of sales	0	0	0
Benefits and losses	162,426	86,064	169,328
Amortization of deferred policy acquisition costs	31,219	28,556	24,514
Lease expense	0	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	215,070	129,233	215,903
Earnings from operations before equity in earnings of subsidiaries	26,394	25,481	27,959
Equity in earnings of subsidiaries	0	0	0
Earnings from operations	26,394	25,481	27,959
Other components of net periodic benefit costs	0	0	0
Interest expense	0	0	0
Pretax earnings	26,394	25,481	27,959
Income tax expense	(4,533)	(5,378)	(3,858)
Earnings available to common shareholders	21,861	20,103	24,101
Eliminations [Member]
Revenues:
Self-moving equipment rentals	(4,103)	(2,830)	(4,214)
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	(3,088)	(2,635)	(1,700)
Net investment and interest income	(1,705)	(1,667)	(1,688)
Other revenue	(530)	(521)	(384)
Total revenues	(9,426)	(7,653)	(7,986)
Costs and expenses:
Operating expenses	(7,702)	(5,968)	(6,412)
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	(612)	(544)	(283)
Depreciation, net of (gains) losses on disposals	0	0	0
Net gains on disposal of real estate	0	0	0
Total costs and expenses	(8,314)	(6,512)	(6,695)
Earnings from operations before equity in earnings of subsidiaries	(1,112)	(1,141)	(1,291)
Equity in earnings of subsidiaries	(55,789)	(41,811)	(46,990)
Earnings from operations	(56,901)	(42,952)	(48,281)
Other components of net periodic benefit costs	0	0	0
Interest expense	1,112	1,141	1,291
Pretax earnings	(55,789)	(41,811)	(46,990)
Income tax expense	0	0	0
Earnings available to common shareholders	$ (55,789)	$ (41,811)	$ (46,990)