Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Revenues:
Self-moving equipment rentals	$ 975,552	$ 808,215	$ 3,189,990	$ 2,393,530
Self-storage revenues	159,424	123,024	450,302	347,252
Self moving and self-storage products and service sales	75,402	74,586	272,478	264,564
Property management fees	9,651	8,765	26,847	23,952
Life insurance premiums	27,010	29,993	84,628	91,958
Property and casualty insurance premiums	25,618	19,933	64,986	49,536
Net investment and interest income	31,184	35,580	102,963	85,895
Other revenue	100,495	69,886	349,252	225,440
Total revenues	1,404,336	1,169,982	4,541,446	3,482,127
Costs and expenses:
Operating expenses	658,095	539,942	1,968,698	1,606,687
Commission expenses	105,155	86,891	346,200	255,431
Cost of sales	57,042	45,752	193,448	159,516
Benefits and losses	47,266	45,631	139,194	130,660
Amortization of deferred policy acquisition costs	7,947	6,572	23,520	19,012
Lease expense	7,394	7,522	22,482	20,995
Depreciation, net of (gains) losses on disposals	103,736	152,602	361,201	455,711
Net (gains) losses on disposal of real estate	977	1,124	(2,930)	4,293
Total costs and expenses	987,612	886,036	3,051,813	2,652,305
Earnings (loss) from operations before equity in earnings of subsidiaries	416,724	283,946	1,489,633	829,822
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	416,724	283,946	1,489,633	829,822
Other components of net periodic benefit costs	(280)	(247)	(840)	(740)
Interest expense	(44,042)	(42,128)	(122,765)	(122,174)
Fees on early extinguishment of debt	(956)	0	(956)	0
Pretax earnings	371,446	241,571	1,365,072	706,908
Income tax expense	(89,980)	(58,586)	(328,533)	(169,832)
Earnings available to common stockholders	281,466	182,985	1,036,539	537,076
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	977,052	809,371	3,193,594	2,396,098
Self-storage revenues	159,424	123,024	450,302	347,252
Self moving and self-storage products and service sales	75,402	74,586	272,478	264,564
Property management fees	9,651	8,765	26,847	23,952
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	666	524	2,021	1,781
Other revenue	99,385	69,011	346,591	223,252
Total revenues	1,321,580	1,085,281	4,291,833	3,256,899
Costs and expenses:
Operating expenses	642,900	526,884	1,927,060	1,569,763
Commission expenses	105,155	86,891	346,200	255,431
Cost of sales	57,042	45,752	193,448	159,516
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	7,917	8,024	24,018	22,564
Depreciation, net of (gains) losses on disposals	103,736	152,602	361,201	455,711
Net (gains) losses on disposal of real estate	977	1,124	(2,930)	4,293
Total costs and expenses	917,727	821,277	2,848,997	2,467,278
Earnings (loss) from operations before equity in earnings of subsidiaries	403,853	264,004	1,442,836	789,621
Equity in earnings of subsidiaries	10,403	16,117	37,811	32,850
Earnings from operations	414,256	280,121	1,480,647	822,471
Other components of net periodic benefit costs	(280)	(247)	(840)	(740)
Interest expense	(44,311)	(42,401)	(123,568)	(122,995)
Fees on early extinguishment of debt	(956)		(956)
Pretax earnings	368,709	237,473	1,355,283	698,736
Income tax expense	(87,243)	(54,488)	(318,744)	(161,660)
Earnings available to common stockholders	281,466	182,985	1,036,539	537,076
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0	0
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	26,477	20,706	67,277	51,934
Net investment and interest income	3,343	5,934	15,538	11,013
Other revenue	0	0	0	0
Total revenues	29,820	26,640	82,815	62,947
Costs and expenses:
Operating expenses	12,198	10,072	31,779	27,063
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	7,892	4,908	16,679	11,376
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	73	169	279	170
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	20,163	15,149	48,737	38,609
Earnings (loss) from operations before equity in earnings of subsidiaries	9,657	11,491	34,078	24,338
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	9,657	11,491	34,078	24,338
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Fees on early extinguishment of debt	0		0
Pretax earnings	9,657	11,491	34,078	24,338
Income tax expense	(2,027)	(2,405)	(7,133)	(5,121)
Earnings available to common stockholders	7,630	9,086	26,945	19,217
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0	0
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	27,010	29,993	84,628	91,958
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	28,182	30,092	88,448	75,749
Other revenue	1,225	992	2,985	2,583
Total revenues	56,417	61,077	176,061	170,290
Costs and expenses:
Operating expenses	5,465	5,027	16,063	15,208
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	39,374	40,723	122,515	119,284
Amortization of deferred policy acquisition costs	7,947	6,572	23,520	19,012
Lease expense	28	31	81	102
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	52,814	52,353	162,179	153,606
Earnings (loss) from operations before equity in earnings of subsidiaries	3,603	8,724	13,882	16,684
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	3,603	8,724	13,882	16,684
Other components of net periodic benefit costs	0	0	0	0
Interest expense	(120)	0	(360)	0
Fees on early extinguishment of debt	0		0
Pretax earnings	3,483	8,724	13,522	16,684
Income tax expense	(710)	(1,693)	(2,656)	(3,051)
Earnings available to common stockholders	2,773	7,031	10,866	13,633
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(1,500)	(1,156)	(3,604)	(2,568)
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	(859)	(773)	(2,291)	(2,398)
Net investment and interest income	(1,007)	(970)	(3,044)	(2,648)
Other revenue	(115)	(117)	(324)	(395)
Total revenues	(3,481)	(3,016)	(9,263)	(8,009)
Costs and expenses:
Operating expenses	(2,468)	(2,041)	(6,204)	(5,347)
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	(624)	(702)	(1,896)	(1,841)
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	(3,092)	(2,743)	(8,100)	(7,188)
Earnings (loss) from operations before equity in earnings of subsidiaries	(389)	(273)	(1,163)	(821)
Equity in earnings of subsidiaries	(10,403)	(16,117)	(37,811)	(32,850)
Earnings from operations	(10,792)	(16,390)	(38,974)	(33,671)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	389	273	1,163	821
Fees on early extinguishment of debt	0		0
Pretax earnings	(10,403)	(16,117)	(37,811)	(32,850)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (10,403)	$ (16,117)	$ (37,811)	$ (32,850)