Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Self-moving equipment rentals	$ 748,596	$ 716,602
Self-storage revenues	98,274	86,212
Self moving and self-storage products and service sales	80,026	79,241
Property management fees	7,156	7,416
Life insurance premiums	32,710	36,888
Property and casualty insurance premiums	13,424	12,781
Net investment and interest income	35,749	24,605
Other revenue	63,314	55,832
Total revenues	1,079,249	1,019,577
Costs and expenses:
Operating expenses	534,472	496,554
Commission expenses	80,899	79,257
Cost of sales	48,929	49,881
Benefits and losses	49,006	48,554
Amortization of deferred policy acquisition costs	6,064	6,031
Lease expense	7,036	8,169
Depreciation, net of (gains) losses on disposals	140,600	126,427
Net (gains) losses on disposal of real estate	(1,622)	0
Total costs and expenses	865,384	814,873
Earnings (loss) from operations before equity in earnings of subsidiaries	213,865	204,704
Equity in earnings of subsidiaries	0	0
Earnings from operations	213,865	204,704
Pretax earnings	174,714	169,197
Earnings available to common stockholders	132,422	127,849
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	749,136	717,542
Self-storage revenues	98,274	86,212
Self moving and self-storage products and service sales	80,026	79,241
Property management fees	7,156	7,416
Life insurance premiums	0	0
Property and casualty insurance premiums	0	0
Net investment and interest income	3,267	2,563
Other revenue	62,539	54,911
Total revenues	1,000,398	947,885
Costs and expenses:
Operating expenses	522,524	483,620
Commission expenses	80,899	79,257
Cost of sales	48,929	49,881
Benefits and losses	0	0
Amortization of deferred policy acquisition costs	0	0
Lease expense	7,172	8,305
Depreciation, net of (gains) losses on disposals	140,600	126,427
Net (gains) losses on disposal of real estate	(1,622)	0
Total costs and expenses	798,502	747,490
Earnings (loss) from operations before equity in earnings of subsidiaries	201,896	200,395
Equity in earnings of subsidiaries	9,831	3,656
Earnings from operations	211,727	204,051
Other components of net periodic benefit costs	(263)	(253)
Interest expense	(39,166)	(35,539)
Pretax earnings	172,298	168,259
Income tax expense	(39,876)	(40,410)
Earnings available to common stockholders	132,422	127,849
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0
Self-storage revenues	0	0
Self moving and self-storage products and service sales	0	0
Property management fees	0	0
Life insurance premiums	0	0
Property and casualty insurance premiums	14,114	13,348
Net investment and interest income	6,191	2,541
Other revenue	0	0
Total revenues	20,305	15,889
Costs and expenses:
Operating expenses	8,081	8,700
Commission expenses	0	0
Cost of sales	0	0
Benefits and losses	3,758	4,476
Amortization of deferred policy acquisition costs	0	0
Lease expense	0	0
Depreciation, net of (gains) losses on disposals	0	0
Net (gains) losses on disposal of real estate	0	0
Total costs and expenses	11,839	13,176
Earnings (loss) from operations before equity in earnings of subsidiaries	8,466	2,713
Equity in earnings of subsidiaries	0	0
Earnings from operations	8,466	2,713
Other components of net periodic benefit costs	0	0
Interest expense	0	0
Pretax earnings	8,466	2,713
Income tax expense	(1,778)	(545)
Earnings available to common stockholders	6,688	2,168
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0
Self-storage revenues	0	0
Self moving and self-storage products and service sales	0	0
Property management fees	0	0
Life insurance premiums	32,710	36,888
Property and casualty insurance premiums	0	0
Net investment and interest income	26,701	19,917
Other revenue	910	1,058
Total revenues	60,321	57,863
Costs and expenses:
Operating expenses	5,228	5,873
Commission expenses	0	0
Cost of sales	0	0
Benefits and losses	45,248	44,078
Amortization of deferred policy acquisition costs	6,064	6,031
Lease expense	0	0
Depreciation, net of (gains) losses on disposals	0	0
Net (gains) losses on disposal of real estate	0	0
Total costs and expenses	56,540	55,982
Earnings (loss) from operations before equity in earnings of subsidiaries	3,781	1,881
Equity in earnings of subsidiaries	0	0
Earnings from operations	3,781	1,881
Other components of net periodic benefit costs	0	0
Interest expense	0	0
Pretax earnings	3,781	1,881
Income tax expense	(638)	(393)
Earnings available to common stockholders	3,143	1,488
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(540)	(940)
Self-storage revenues	0	0
Self moving and self-storage products and service sales	0	0
Property management fees	0	0
Life insurance premiums	0	0
Property and casualty insurance premiums	(690)	(567)
Net investment and interest income	(410)	(416)
Other revenue	(135)	(137)
Total revenues	(1,775)	(2,060)
Costs and expenses:
Operating expenses	(1,361)	(1,639)
Commission expenses	0	0
Cost of sales	0	0
Benefits and losses	0	0
Amortization of deferred policy acquisition costs	0	0
Lease expense	(136)	(136)
Depreciation, net of (gains) losses on disposals	0	0
Net (gains) losses on disposal of real estate	0	0
Total costs and expenses	(1,497)	(1,775)
Earnings (loss) from operations before equity in earnings of subsidiaries	(278)	(285)
Equity in earnings of subsidiaries	(9,831)	(3,656)
Earnings from operations	(10,109)	(3,941)
Other components of net periodic benefit costs	0	0
Interest expense	278	285
Pretax earnings	(9,831)	(3,656)
Income tax expense	0	0
Earnings available to common stockholders	$ (9,831)	$ (3,656)