Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Self-moving equipment rentals	$ 621,471	$ 626,136	$ 2,174,392	$ 2,124,451
Self-storage revenues	106,701	93,392	309,940	271,097
Self moving and self-storage products and service sales	54,454	55,665	207,601	207,819
Property management fees	9,098	7,899	23,487	22,507
Life insurance premiums	31,164	34,778	96,229	107,586
Property and casualty insurance premiums	19,267	17,668	51,056	46,732
Net investment and interest income	33,782	32,211	102,629	85,043
Other revenue	51,943	51,342	192,009	177,940
Total revenues	927,880	919,091	3,157,343	3,043,175
Costs and expenses:
Operating expenses	517,453	478,461	1,617,338	1,504,365
Commission expenses	66,542	67,493	233,540	232,084
Cost of sales	35,318	34,149	128,177	130,432
Benefits and losses	42,864	42,869	137,695	137,196
Amortization of deferred policy acquisition costs	8,046	6,654	20,625	18,584
Lease expense	6,490	7,890	19,882	24,229
Depreciation, net of (gains) losses on disposals	170,074	143,473	462,227	402,525
Net (gains) losses on disposal of real estate	528	0	(1,311)	10
Total costs and expenses	847,315	780,989	2,618,173	2,449,425
Earnings (loss) from operations before equity in earnings of subsidiaries	80,565	138,102	539,170	593,750
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	80,565	138,102	539,170	593,750
Pretax earnings	40,329	103,022	420,397	487,879
Earnings available to common stockholders	30,932	78,635	319,680	370,026
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	622,902	627,543	2,177,697	2,128,120
Self-storage revenues	106,701	93,392	309,940	271,097
Self moving and self-storage products and service sales	54,454	55,665	207,601	207,819
Property management fees	9,098	7,899	23,487	22,507
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	2,351	4,364	8,649	9,757
Other revenue	50,858	50,065	188,940	174,447
Total revenues	846,364	838,928	2,916,314	2,813,747
Costs and expenses:
Operating expenses	505,473	465,828	1,580,705	1,467,831
Commission expenses	66,542	67,493	233,540	232,084
Cost of sales	35,318	34,149	128,177	130,432
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	6,660	8,026	20,324	24,637
Depreciation, net of (gains) losses on disposals	170,074	143,473	462,227	402,525
Net (gains) losses on disposal of real estate	528		(1,311)	10
Total costs and expenses	784,595	718,969	2,423,662	2,257,519
Earnings (loss) from operations before equity in earnings of subsidiaries	61,769	119,959	492,652	556,228
Equity in earnings of subsidiaries	15,196	14,664	37,941	30,306
Earnings from operations	76,965	134,623	530,593	586,534
Other components of net periodic benefit costs	(263)	(253)	(790)	(760)
Interest expense	(40,251)	(35,114)	(118,819)	(105,974)
Pretax earnings	36,451	99,256	410,984	479,800
Income tax expense	(5,519)	(20,621)	(91,304)	(109,774)
Earnings available to common stockholders	30,932	78,635	319,680	370,026
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	20,040	18,128	53,370	48,448
Net investment and interest income	5,326	4,018	15,829	10,109
Other revenue	0	0	0	0
Total revenues	25,366	22,146	69,199	58,557
Costs and expenses:
Operating expenses	9,309	9,412	26,785	26,027
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	6,173	1,733	14,972	10,957
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	0	0	0	0
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0		0	0
Total costs and expenses	15,482	11,145	41,757	36,984
Earnings (loss) from operations before equity in earnings of subsidiaries	9,884	11,001	27,442	21,573
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	9,884	11,001	27,442	21,573
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	9,884	11,001	27,442	21,573
Income tax expense	(2,083)	(2,186)	(5,725)	(4,359)
Earnings available to common stockholders	7,801	8,815	21,717	17,214
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	31,164	34,778	96,229	107,586
Property and casualty insurance premiums	0	0	0	0
Net investment and interest income	26,550	24,248	79,416	66,435
Other revenue	1,175	1,409	3,424	3,889
Total revenues	58,889	60,435	179,069	177,910
Costs and expenses:
Operating expenses	4,962	5,216	15,809	16,275
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	36,691	41,136	122,723	126,239
Amortization of deferred policy acquisition costs	8,046	6,654	20,625	18,584
Lease expense	0	0	0	0
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0		0	0
Total costs and expenses	49,699	53,006	159,157	161,098
Earnings (loss) from operations before equity in earnings of subsidiaries	9,190	7,429	19,912	16,812
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	9,190	7,429	19,912	16,812
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Pretax earnings	9,190	7,429	19,912	16,812
Income tax expense	(1,795)	(1,580)	(3,688)	(3,720)
Earnings available to common stockholders	7,395	5,849	16,224	13,092
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(1,431)	(1,407)	(3,305)	(3,669)
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)	(460)	(2,314)	(1,716)
Net investment and interest income	(445)	(419)	(1,265)	(1,258)
Other revenue	(90)	(132)	(355)	(396)
Total revenues	(2,739)	(2,418)	(7,239)	(7,039)
Costs and expenses:
Operating expenses	(2,291)	(1,995)	(5,961)	(5,768)
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	(170)	(136)	(442)	(408)
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0		0	0
Total costs and expenses	(2,461)	(2,131)	(6,403)	(6,176)
Earnings (loss) from operations before equity in earnings of subsidiaries	(278)	(287)	(836)	(863)
Equity in earnings of subsidiaries	(15,196)	(14,664)	(37,941)	(30,306)
Earnings from operations	(15,474)	(14,951)	(38,777)	(31,169)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	278	287	836	863
Pretax earnings	(15,196)	(14,664)	(37,941)	(30,306)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (15,196)	$ (14,664)	$ (37,941)	$ (30,306)