Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Self-moving equipment rentals	$ 931,030	$ 804,325	$ 1,585,315	$ 1,552,921
Self-storage revenues	115,273	104,965	224,228	203,239
Self moving and self-storage products and service sales	98,628	73,121	189,978	153,147
Property management fees	7,840	7,233	15,187	14,389
Life insurance premiums	31,057	32,355	61,965	65,065
Property and casualty insurance premiums	15,869	18,365	29,603	31,789
Net investment and Interest income	33,333	33,098	50,315	68,847
Other revenue	91,878	76,752	155,554	140,066
Total revenues	1,324,908	1,150,214	2,312,145	2,229,463
Costs and expenses:
Operating expenses	574,083	565,413	1,066,745	1,099,885
Commission expenses	99,365	86,099	168,540	166,998
Cost of sales	60,933	43,930	113,764	92,859
Benefits and losses	45,452	45,825	85,029	94,831
Amortization of deferred policy acquisition costs	5,552	6,515	12,440	12,579
Lease expense	6,870	6,356	13,473	13,392
Depreciation, net of (gains) losses on disposals	137,438	151,553	303,109	292,153
Net (gains) losses on disposal of real estate	3,425	(217)	3,169	(1,839)
Total costs and expenses	933,118	905,474	1,766,269	1,770,858
Earnings (loss) from operations before equity in earnings of subsidiaries	391,790	244,740	545,876	458,605
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	391,790	244,740	545,876	458,605
Other components of net periodic benefit costs	(246)	(264)	(493)	(527)
Interest expense	(40,525)	(39,122)	(80,046)	(78,010)
Pretax earnings	351,019	205,354	465,337	380,068
Income tax expense	(84,654)	(49,028)	(111,246)	(91,320)
Earnings available to common stockholders	266,365	156,326	354,091	288,748
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	931,814	805,659	1,586,727	1,554,795
Self-storage revenues	115,273	104,965	224,228	203,239
Self moving and self-storage products and service sales	98,628	73,121	189,978	153,147
Property management fees	7,840	7,233	15,187	14,389
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	595	3,031	1,257	6,298
Other revenue	91,168	75,543	154,241	138,082
Total revenues	1,245,318	1,069,552	2,171,618	2,069,950
Costs and expenses:
Operating expenses	562,798	552,708	1,042,879	1,075,232
Commission expenses	99,365	86,099	168,540	166,998
Cost of sales	60,933	43,930	113,764	92,859
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	7,403	6,492	14,540	13,664
Depreciation, net of (gains) losses on disposals	137,438	151,553	303,109	292,153
Net (gains) losses on disposal of real estate	3,425	(217)	3,169	(1,839)
Total costs and expenses	871,362	840,565	1,646,001	1,639,067
Earnings (loss) from operations before equity in earnings of subsidiaries	373,956	228,987	525,617	430,883
Equity in earnings of subsidiaries	14,338	12,914	16,733	22,745
Earnings from operations	388,294	241,901	542,350	453,628
Other components of net periodic benefit costs	(246)	(264)	(493)	(527)
Interest expense	(40,800)	(39,402)	(80,594)	(78,568)
Pretax earnings	347,248	202,235	461,263	374,533
Income tax expense	(80,883)	(45,909)	(107,172)	(85,785)
Earnings available to common stockholders	266,365	156,326	354,091	288,748
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	16,721	19,216	31,228	33,330
Net investment and Interest income	5,952	4,312	5,079	10,503
Other revenue	0	0	0	0
Total revenues	22,673	23,528	36,307	43,833
Costs and expenses:
Operating expenses	8,166	9,395	16,991	17,476
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	2,438	5,041	6,468	8,799
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	0	0	1	0
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	10,604	14,436	23,460	26,275
Earnings (loss) from operations before equity in earnings of subsidiaries	12,069	9,092	12,847	17,558
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	12,069	9,092	12,847	17,558
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	12,069	9,092	12,847	17,558
Income tax expense	(2,554)	(1,864)	(2,716)	(3,642)
Earnings available to common stockholders	9,515	7,228	10,131	13,916
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	31,057	32,355	61,965	65,065
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	27,651	26,165	45,657	52,866
Other revenue	852	1,339	1,591	2,249
Total revenues	59,560	59,859	109,213	120,180
Costs and expenses:
Operating expenses	4,893	5,619	10,181	10,847
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	43,014	40,784	78,561	86,032
Amortization of deferred policy acquisition costs	5,552	6,515	12,440	12,579
Lease expense	61	0	71	0
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	53,520	52,918	101,253	109,458
Earnings (loss) from operations before equity in earnings of subsidiaries	6,040	6,941	7,960	10,722
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	6,040	6,941	7,960	10,722
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	6,040	6,941	7,960	10,722
Income tax expense	(1,217)	(1,255)	(1,358)	(1,893)
Earnings available to common stockholders	4,823	5,686	6,602	8,829
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(784)	(1,334)	(1,412)	(1,874)
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	(852)	(851)	(1,625)	(1,541)
Net investment and Interest income	(865)	(410)	(1,678)	(820)
Other revenue	(142)	(130)	(278)	(265)
Total revenues	(2,643)	(2,725)	(4,993)	(4,500)
Costs and expenses:
Operating expenses	(1,774)	(2,309)	(3,306)	(3,670)
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	(594)	(136)	(1,139)	(272)
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	(2,368)	(2,445)	(4,445)	(3,942)
Earnings (loss) from operations before equity in earnings of subsidiaries	(275)	(280)	(548)	(558)
Equity in earnings of subsidiaries	(14,338)	(12,914)	(16,733)	(22,745)
Earnings from operations	(14,613)	(13,194)	(17,281)	(23,303)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	275	280	548	558
Pretax earnings	(14,338)	(12,914)	(16,733)	(22,745)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (14,338)	$ (12,914)	$ (16,733)	$ (22,745)