Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Self-moving equipment rentals	$ 1,179,061	$ 931,030	$ 2,214,438	$ 1,585,315
Self-storage revenues	153,485	115,273	290,878	224,228
Self moving and self-storage products and service sales	92,191	98,628	197,076	189,978
Property management fees	8,747	7,840	17,196	15,187
Life insurance premiums	28,913	31,057	57,618	61,965
Property and casualty insurance premiums	22,499	15,869	39,368	29,603
Net investment and Interest income	36,780	33,333	71,779	50,315
Other revenue	142,578	91,878	248,757	155,554
Total revenues	1,664,254	1,324,908	3,137,110	2,312,145
Costs and expenses:
Operating expenses	696,074	574,083	1,310,603	1,066,745
Commission expenses	127,896	99,365	241,045	168,540
Cost of sales	66,491	60,933	136,406	113,764
Benefits and losses	44,630	45,452	91,928	85,029
Amortization of deferred policy acquisition costs	6,750	5,552	15,573	12,440
Lease expense	7,441	6,870	15,088	13,473
Depreciation, net of (gains) losses on disposals	135,748	137,438	257,465	303,109
Net (gains) losses on disposal of real estate	523	3,425	(3,907)	3,169
Total costs and expenses	1,085,553	933,118	2,064,201	1,766,269
Earnings (loss) from operations before equity in earnings of subsidiaries	578,701	391,790	1,072,909	545,876
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	578,701	391,790	1,072,909	545,876
Other components of net periodic benefit costs	(280)	(246)	(560)	(493)
Interest expense	(39,545)	(40,525)	(78,723)	(80,046)
Pretax earnings	538,876	351,019	993,626	465,337
Income tax expense	(128,978)	(84,654)	(238,553)	(111,246)
Earnings available to common stockholders	409,898	266,365	755,073	354,091
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	1,180,329	931,814	2,216,542	1,586,727
Self-storage revenues	153,485	115,273	290,878	224,228
Self moving and self-storage products and service sales	92,191	98,628	197,076	189,978
Property management fees	8,747	7,840	17,196	15,187
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	675	595	1,355	1,257
Other revenue	141,572	91,168	247,206	154,241
Total revenues	1,576,999	1,245,318	2,970,253	2,171,618
Costs and expenses:
Operating expenses	682,329	562,798	1,284,160	1,042,879
Commission expenses	127,896	99,365	241,045	168,540
Cost of sales	66,491	60,933	136,406	113,764
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	8,024	7,403	16,101	14,540
Depreciation, net of (gains) losses on disposals	135,748	137,438	257,465	303,109
Net (gains) losses on disposal of real estate	523	3,425	(3,907)	3,169
Total costs and expenses	1,021,011	871,362	1,931,270	1,646,001
Earnings (loss) from operations before equity in earnings of subsidiaries	555,988	373,956	1,038,983	525,617
Equity in earnings of subsidiaries	18,289	14,338	27,408	16,733
Earnings from operations	574,277	388,294	1,066,391	542,350
Other components of net periodic benefit costs	(280)	(246)	(560)	(493)
Interest expense	(39,814)	(40,800)	(79,257)	(80,594)
Pretax earnings	534,183	347,248	986,574	461,263
Income tax expense	(124,285)	(80,883)	(231,501)	(107,172)
Earnings available to common stockholders	409,898	266,365	755,073	354,091
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	23,357	16,721	40,800	31,228
Net investment and Interest income	6,182	5,952	12,195	5,079
Other revenue	0	0	0	0
Total revenues	29,539	22,673	52,995	36,307
Costs and expenses:
Operating expenses	10,768	8,166	19,581	16,991
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	3,560	2,438	8,787	6,468
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	22	0	206	1
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	14,350	10,604	28,574	23,460
Earnings (loss) from operations before equity in earnings of subsidiaries	15,189	12,069	24,421	12,847
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	15,189	12,069	24,421	12,847
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	15,189	12,069	24,421	12,847
Income tax expense	(3,176)	(2,554)	(5,106)	(2,716)
Earnings available to common stockholders	12,013	9,515	19,315	10,131
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	28,913	31,057	57,618	61,965
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	30,942	27,651	60,266	45,657
Other revenue	1,130	852	1,760	1,591
Total revenues	60,985	59,560	119,644	109,213
Costs and expenses:
Operating expenses	5,223	4,893	10,598	10,181
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	41,070	43,014	83,141	78,561
Amortization of deferred policy acquisition costs	6,750	5,552	15,573	12,440
Lease expense	29	61	53	71
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	53,072	53,520	109,365	101,253
Earnings (loss) from operations before equity in earnings of subsidiaries	7,913	6,040	10,279	7,960
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	7,913	6,040	10,279	7,960
Other components of net periodic benefit costs	0	0	0	0
Interest expense	(120)	0	(240)	0
Pretax earnings	7,793	6,040	10,039	7,960
Income tax expense	(1,517)	(1,217)	(1,946)	(1,358)
Earnings available to common stockholders	6,276	4,823	8,093	6,602
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(1,268)	(784)	(2,104)	(1,412)
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	(858)	(852)	(1,432)	(1,625)
Net investment and Interest income	(1,019)	(865)	(2,037)	(1,678)
Other revenue	(124)	(142)	(209)	(278)
Total revenues	(3,269)	(2,643)	(5,782)	(4,993)
Costs and expenses:
Operating expenses	(2,246)	(1,774)	(3,736)	(3,306)
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	(634)	(594)	(1,272)	(1,139)
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	(2,880)	(2,368)	(5,008)	(4,445)
Earnings (loss) from operations before equity in earnings of subsidiaries	(389)	(275)	(774)	(548)
Equity in earnings of subsidiaries	(18,289)	(14,338)	(27,408)	(16,733)
Earnings from operations	(18,678)	(14,613)	(28,182)	(17,281)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	389	275	774	548
Pretax earnings	(18,289)	(14,338)	(27,408)	(16,733)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (18,289)	$ (14,338)	$ (27,408)	$ (16,733)