Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Self-moving equipment rentals	$ 808,215	$ 621,471	$ 2,393,530	$ 2,174,392
Self-storage revenues	123,024	106,701	347,252	309,940
Self moving and self-storage products and service sales	74,586	54,454	264,564	207,601
Property management fees	8,765	9,098	23,952	23,487
Life insurance premiums	29,993	31,164	91,958	96,229
Property and casualty insurance premiums	19,933	19,267	49,536	51,056
Net investment and interest income	35,580	33,782	85,895	102,629
Other revenue	69,886	51,943	225,440	192,009
Total revenues	1,169,982	927,880	3,482,127	3,157,343
Costs and expenses:
Operating expenses	539,942	517,453	1,606,687	1,617,338
Commission expenses	86,891	66,542	255,431	233,540
Cost of sales	45,752	35,318	159,516	128,177
Benefits and losses	45,631	42,864	130,660	137,695
Amortization of deferred policy acquisition costs	6,572	8,046	19,012	20,625
Lease expense	7,522	6,490	20,995	19,882
Depreciation, net of (gains) losses on disposals	152,602	170,074	455,711	462,227
Net (gains) losses on disposal of real estate	1,124	528	4,293	(1,311)
Total costs and expenses	886,036	847,315	2,652,305	2,618,173
Earnings (loss) from operations before equity in earnings of subsidiaries	283,946	80,565	829,822	539,170
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	283,946	80,565	829,822	539,170
Other components of net periodic benefit costs	(247)	(263)	(740)	(790)
Interest expense	(42,128)	(39,973)	(122,174)	(117,983)
Pretax earnings	241,571	40,329	706,908	420,397
Income tax expense	(58,586)	(9,397)	(169,832)	(100,717)
Earnings available to common stockholders	182,985	30,932	537,076	319,680
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	809,371	622,902	2,396,098	2,177,697
Self-storage revenues	123,024	106,701	347,252	309,940
Self moving and self-storage products and service sales	74,586	54,454	264,564	207,601
Property management fees	8,765	9,098	23,952	23,487
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	524	2,351	1,781	8,649
Other revenue	69,011	50,858	223,252	188,940
Total revenues	1,085,281	846,364	3,256,899	2,916,314
Costs and expenses:
Operating expenses	526,884	505,473	1,569,763	1,580,705
Commission expenses	86,891	66,542	255,431	233,540
Cost of sales	45,752	35,318	159,516	128,177
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	8,024	6,660	22,564	20,324
Depreciation, net of (gains) losses on disposals	152,602	170,074	455,711	462,227
Net (gains) losses on disposal of real estate	1,124	528	4,293	(1,311)
Total costs and expenses	821,277	784,595	2,467,278	2,423,662
Earnings (loss) from operations before equity in earnings of subsidiaries	264,004	61,769	789,621	492,652
Equity in earnings of subsidiaries	16,117	15,196	32,850	37,941
Earnings from operations	280,121	76,965	822,471	530,593
Other components of net periodic benefit costs	(247)	(263)	(740)	(790)
Interest expense	(42,401)	(40,251)	(122,995)	(118,819)
Pretax earnings	237,473	36,451	698,736	410,984
Income tax expense	(54,488)	(5,519)	(161,660)	(91,304)
Earnings available to common stockholders	182,985	30,932	537,076	319,680
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	20,706	20,040	51,934	53,370
Net investment and interest income	5,934	5,326	11,013	15,829
Other revenue	0	0	0	0
Total revenues	26,640	25,366	62,947	69,199
Costs and expenses:
Operating expenses	10,072	9,309	27,063	26,785
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	4,908	6,173	11,376	14,972
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	169	0	170	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	15,149	15,482	38,609	41,757
Earnings (loss) from operations before equity in earnings of subsidiaries	11,491	9,884	24,338	27,442
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	11,491	9,884	24,338	27,442
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	11,491	9,884	24,338	27,442
Income tax expense	(2,405)	(2,083)	(5,121)	(5,725)
Earnings available to common stockholders	9,086	7,801	19,217	21,717
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	29,993	31,164	91,958	96,229
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	30,092	26,550	75,749	79,416
Other revenue	992	1,175	2,583	3,424
Total revenues	61,077	58,889	170,290	179,069
Costs and expenses:
Operating expenses	5,027	4,962	15,208	15,809
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	40,723	36,691	119,284	122,723
Amortization of deferred policy acquisition costs	6,572	8,046	19,012	20,625
Lease expense	31	0	102	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	52,353	49,699	153,606	159,157
Earnings (loss) from operations before equity in earnings of subsidiaries	8,724	9,190	16,684	19,912
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	8,724	9,190	16,684	19,912
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	8,724	9,190	16,684	19,912
Income tax expense	(1,693)	(1,795)	(3,051)	(3,688)
Earnings available to common stockholders	7,031	7,395	13,633	16,224
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(1,156)	(1,431)	(2,568)	(3,305)
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	(773)	(773)	(2,398)	(2,314)
Net investment and interest income	(970)	(445)	(2,648)	(1,265)
Other revenue	(117)	(90)	(395)	(355)
Total revenues	(3,016)	(2,739)	(8,009)	(7,239)
Costs and expenses:
Operating expenses	(2,041)	(2,291)	(5,347)	(5,961)
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	(702)	(170)	(1,841)	(442)
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	(2,743)	(2,461)	(7,188)	(6,403)
Earnings (loss) from operations before equity in earnings of subsidiaries	(273)	(278)	(821)	(836)
Equity in earnings of subsidiaries	(16,117)	(15,196)	(32,850)	(37,941)
Earnings from operations	(16,390)	(15,474)	(33,671)	(38,777)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	273	278	821	836
Pretax earnings	(16,117)	(15,196)	(32,850)	(37,941)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (16,117)	$ (15,196)	$ (32,850)	$ (37,941)