Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended
		Jun. 30, 2018		Jun. 30, 2017
Revenues:
Self-moving equipment rentals		$ 716,602		$ 669,858
Self-storage revenues		86,212		76,718
Self-moving and self-storage products and service sales		79,241		78,911
Property management fees		7,416		6,762
Life insurance premiums		36,888		39,091
Property and casualty insurance premiums		12,781		11,815
Net investment and interest income		24,605		27,217
Other revenue		55,832		47,553
Total revenues		1,019,577		957,925
Costs and expenses:
Operating expenses		496,554		416,692
Commission expenses		79,257		75,365
Cost of sales		49,881		47,595
Benefits and losses		48,554		47,720
Amortization of deferred policy acquisition costs		6,031		6,321
Lease expense		8,169		8,287
Depreciation, net of (gains) losses on disposals		126,427		126,335
Net (gains) losses on disposal of real estate				347
Total costs and expenses		814,873		728,662
Earnings (loss) from operations before equity in earnings of subsidiaries		204,704		229,263
Equity in earnings of subsidiaries
Earnings from operations		204,704		229,263
Other components of net periodic benefit costs		(253)		(232)
Interest expense		(35,254)		(30,345)
Pretax earnings		169,197		198,686
Income tax expense		(41,348)		(72,479)
Earnings available to common stockholders		127,849		126,207
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals		717,542		670,698
Self-storage revenues		86,212		76,718
Self-moving and self-storage products and service sales		79,241		78,911
Property management fees		7,416		6,762
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income		2,563		2,657
Other revenue		54,911		46,781
Total revenues		947,885		882,527
Costs and expenses:
Operating expenses		483,620		403,811
Commission expenses		79,257		75,365
Cost of sales		49,881		47,595
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense		8,305		8,334
Depreciation, net of (gains) losses on disposals		126,427		126,335
Net (gains) losses on disposal of real estate				347
Total costs and expenses		747,490		661,787
Earnings (loss) from operations before equity in earnings of subsidiaries		200,395		220,740
Equity in earnings of subsidiaries		3,656		5,810
Earnings from operations		204,051		226,550
Other components of net periodic benefit costs		(253)		(232)
Interest expense		(35,539)		(30,694)
Pretax earnings		168,259		195,624
Income tax expense		(40,410)		(69,417)
Earnings available to common stockholders		127,849		126,207
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]
Self-storage revenues			[1]		[2]
Self-moving and self-storage products and service sales			[1]		[2]
Property management fees			[1]		[2]
Life insurance premiums			[1]		[2]
Property and casualty insurance premiums		13,348	[1]	11,815	[2]
Net investment and interest income		2,541	[1]	4,291	[2]
Other revenue			[1]		[2]
Total revenues		15,889	[1]	16,106	[2]
Costs and expenses:
Operating expenses		8,700	[1]	8,232	[2]
Commission expenses			[1]		[2]
Cost of sales			[1]		[2]
Benefits and losses		4,476	[1]	2,438	[2]
Amortization of deferred policy acquisition costs			[1]		[2]
Lease expense			[1]		[2]
Depreciation, net of (gains) losses on disposals			[1]		[2]
Net (gains) losses on disposal of real estate
Total costs and expenses		13,176	[1]	10,670	[2]
Earnings (loss) from operations before equity in earnings of subsidiaries		2,713	[1]	5,436	[2]
Equity in earnings of subsidiaries			[1]		[2]
Earnings from operations		2,713	[1]	5,436	[2]
Other components of net periodic benefit costs			[1]		[2]
Interest expense			[1]		[2]
Pretax earnings		2,713	[1]	5,436	[2]
Income tax expense		(545)	[1]	(1,862)	[2]
Earnings available to common stockholders		2,168	[1]	3,574	[2]
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]
Self-storage revenues			[1]		[2]
Self-moving and self-storage products and service sales			[1]		[2]
Property management fees			[1]		[2]
Life insurance premiums		36,888	[1]	39,091	[2]
Property and casualty insurance premiums			[1]		[2]
Net investment and interest income		19,917	[1]	20,655	[2]
Other revenue		1,058	[1]	910	[2]
Total revenues		57,863	[1]	60,656	[2]
Costs and expenses:
Operating expenses		5,873	[1]	5,617	[2]
Commission expenses			[1]		[2]
Cost of sales			[1]		[2]
Benefits and losses		44,078	[1]	45,282	[2]
Amortization of deferred policy acquisition costs		6,031	[1]	6,321	[2]
Lease expense			[1]		[2]
Depreciation, net of (gains) losses on disposals			[1]		[2]
Net (gains) losses on disposal of real estate
Total costs and expenses		55,982	[1]	57,220	[2]
Earnings (loss) from operations before equity in earnings of subsidiaries		1,881	[1]	3,436	[2]
Equity in earnings of subsidiaries			[1]		[2]
Earnings from operations		1,881	[1]	3,436	[2]
Other components of net periodic benefit costs			[1]		[2]
Interest expense			[1]		[2]
Pretax earnings		1,881	[1]	3,436	[2]
Income tax expense		(393)	[1]	(1,200)	[2]
Earnings available to common stockholders		1,488	[1]	2,236	[2]
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	[3]	(940)		(840)
Self-storage revenues
Self-moving and self-storage products and service sales
Property management fees
Life insurance premiums
Property and casualty insurance premiums		(567)
Net investment and interest income	[4]	(416)		(386)
Other revenue	[4]	(137)		(138)
Total revenues		(2,060)		(1,364)
Costs and expenses:
Operating expenses	[3],[4]	(1,639)		(968)
Commission expenses
Cost of sales
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense	[4]	(136)		(47)
Depreciation, net of (gains) losses on disposals
Net (gains) losses on disposal of real estate
Total costs and expenses		(1,775)		(1,015)
Earnings (loss) from operations before equity in earnings of subsidiaries		(285)		(349)
Equity in earnings of subsidiaries	[5]	(3,656)		(5,810)
Earnings from operations		(3,941)		(6,159)
Other components of net periodic benefit costs
Interest expense	[4]	285		349
Pretax earnings		(3,656)		(5,810)
Income tax expense
Earnings available to common stockholders		$ (3,656)		$ (5,810)

[1] Balances for the quarter ended March 31, 2018

[2] Balances for the quarter ended March 31, 2017

[3] Eliminate intercompany premiums

[4] Eliminate intercompany lease / interest income

[5] Eliminate equity in earnings of subsidiaries