Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016
Revenues:
Self-moving equipment rentals		$ 574,801		$ 541,473		$ 1,985,217		$ 1,899,519
Self-storage revenues		82,127		72,309		239,317		212,194
Self-moving and self-storage products and service sales		53,130		51,562		205,309		199,195
Property management fees		9,881		9,734		23,474		23,050
Life insurance premiums		38,957		41,279		116,910		123,064
Property and casualty insurance premiums		16,093		14,938		42,934		40,202
Net investment and interest income		28,821		22,833		82,507		75,754
Other revenue		39,072		36,327		147,825		139,353
Total revenues		842,882		790,455		2,843,493		2,712,331
Costs and expenses:
Operating expenses		438,071		389,352		1,347,477		1,172,647
Commission expenses		63,487		61,052		222,203		215,330
Cost of sales		33,995		32,537		124,456		116,851
Benefits and losses		45,168		45,403		139,997		139,242
Amortization of deferred policy acquisition costs		5,952		5,200		18,217		19,131
Lease expense		8,415		8,807		25,277		29,204
Depreciation, net of (gains) losses on disposals		137,061		118,541		396,540		323,785
Net gains on disposal of real estate		(192,404)		(2,418)		(192,223)		(2,377)
Total costs and expenses		539,745		658,474		2,081,944		2,013,813
Earnings (loss) from operations before equity in earnings of subsidiaries		303,137		131,981		761,549		698,518
Equity in earnings of subsidiaries
Earnings from operations		303,137		131,981		761,549		698,518
Interest expense		(31,558)		(28,782)		(93,926)		(83,197)
Amortization on early extinguishment of debt				(499)				(499)
Pretax earnings		271,579		102,700		667,623		614,822
Income tax expense		257,315		(37,472)		112,117		(225,946)
Earnings available to common shareholders		528,894		65,228		779,740		388,876
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals		576,018		542,545		1,988,430		1,902,400
Self-storage revenues		82,127		72,309		239,317		212,194
Self-moving and self-storage products and service sales		53,130		51,562		205,309		199,195
Property management fees		9,881		9,734		23,474		23,050
Life insurance premiums
Property and casualty insurance premiums
Net investment and interest income		3,662		2,570		9,496		7,035
Other revenue		37,669		35,264		144,196		136,341
Total revenues		762,487		713,984		2,610,222		2,480,215
Costs and expenses:
Operating expenses		426,394		377,165		1,310,892		1,137,364
Commission expenses		63,487		61,052		222,203		215,330
Cost of sales		33,995		32,537		124,456		116,851
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense		8,498		8,854		25,460		29,344
Depreciation, net of (gains) losses on disposals		137,061		118,541		396,540		323,785
Net gains on disposal of real estate		(192,404)		(2,418)		(192,223)		(2,377)
Total costs and expenses		477,031		595,731		1,887,328		1,820,297
Earnings (loss) from operations before equity in earnings of subsidiaries		285,456		118,253		722,894		659,918
Equity in earnings of subsidiaries		11,823		9,046		25,998		25,925
Earnings from operations		297,279		127,299		748,892		685,843
Interest expense		(31,854)		(29,145)		(94,925)		(84,299)
Amortization on early extinguishment of debt				(499)				(499)
Pretax earnings		265,425		97,655		653,967		601,045
Income tax expense		263,469		(32,427)		125,773		(212,169)
Earnings available to common shareholders		528,894		65,228		779,740		388,876
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]		[3]		[4]
Self-storage revenues			[1]		[2]		[3]		[4]
Self-moving and self-storage products and service sales			[1]		[2]		[3]		[4]
Property management fees			[1]		[2]		[3]		[4]
Life insurance premiums			[1]		[2]		[3]		[4]
Property and casualty insurance premiums		16,754	[1]	14,938	[2]	44,067	[3]	40,202	[4]
Net investment and interest income		3,645	[1]	3,443	[2]	11,637	[3]	12,951	[4]
Other revenue			[1]		[2]		[3]		[4]
Total revenues		20,399	[1]	18,381	[2]	55,704	[3]	53,153	[4]
Costs and expenses:
Operating expenses		8,160	[1]	7,688	[2]	24,632	[3]	21,193	[4]
Commission expenses			[1]		[2]		[3]		[4]
Cost of sales			[1]		[2]		[3]		[4]
Benefits and losses		4,644	[1]	3,474	[2]	11,954	[3]	10,144	[4]
Amortization of deferred policy acquisition costs			[1]		[2]		[3]		[4]
Lease expense			[1]		[2]		[3]		[4]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]		[4]
Net gains on disposal of real estate
Total costs and expenses		12,804	[1]	11,162	[2]	36,586	[3]	31,337	[4]
Earnings (loss) from operations before equity in earnings of subsidiaries		7,595	[1]	7,219	[2]	19,118	[3]	21,816	[4]
Equity in earnings of subsidiaries			[1]		[2]		[3]		[4]
Earnings from operations		7,595	[1]	7,219	[2]	19,118	[3]	21,816	[4]
Interest expense			[1]		[2]		[3]		[4]
Amortization on early extinguishment of debt
Pretax earnings		7,595	[1]	7,219	[2]	19,118	[3]	21,816	[4]
Income tax expense		(2,528)	[1]	(2,488)	[2]	(6,481)	[3]	(7,520)	[4]
Earnings available to common shareholders		5,067	[1]	4,731	[2]	12,637	[5]	14,296	[6]
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals			[1]		[2]		[3]		[4]
Self-storage revenues			[1]		[2]		[3]		[4]
Self-moving and self-storage products and service sales			[1]		[2]		[3]		[4]
Property management fees			[1]		[2]		[3]		[4]
Life insurance premiums		38,957	[1]	41,279	[2]	116,910	[3]	123,064	[4]
Property and casualty insurance premiums			[1]		[2]		[3]		[4]
Net investment and interest income		21,887	[1]	17,221	[2]	62,531	[3]	56,982	[4]
Other revenue		1,535	[1]	1,194	[2]	4,024	[3]	3,404	[4]
Total revenues		62,379	[1]	59,694	[2]	183,465	[3]	183,450	[4]
Costs and expenses:
Operating expenses		5,521	[1]	5,693	[2]	16,669	[3]	17,335	[4]
Commission expenses			[1]		[2]		[3]		[4]
Cost of sales			[1]		[2]		[3]		[4]
Benefits and losses		40,524	[1]	41,929	[2]	128,043	[3]	129,098	[4]
Amortization of deferred policy acquisition costs		5,952	[1]	5,200	[2]	18,217	[3]	19,131	[4]
Lease expense			[1]		[2]		[3]		[4]
Depreciation, net of (gains) losses on disposals			[1]		[2]		[3]		[4]
Net gains on disposal of real estate
Total costs and expenses		51,997	[1]	52,822	[2]	162,929	[3]	165,564	[4]
Earnings (loss) from operations before equity in earnings of subsidiaries		10,382	[1]	6,872	[2]	20,536	[3]	17,886	[4]
Equity in earnings of subsidiaries			[1]		[2]		[3]		[4]
Earnings from operations		10,382	[1]	6,872	[2]	20,536	[3]	17,886	[4]
Interest expense			[1]		[2]		[3]		[4]
Amortization on early extinguishment of debt
Pretax earnings		10,382	[1]	6,872	[2]	20,536	[3]	17,886	[4]
Income tax expense		(3,626)	[1]	(2,557)	[2]	(7,175)	[3]	(6,257)	[4]
Earnings available to common shareholders		6,756	[1]	4,315	[2]	13,361	[5]	11,629	[6]
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	[7]	(1,217)		(1,072)		(3,213)		(2,881)
Self-storage revenues
Self-moving and self-storage products and service sales
Property management fees
Life insurance premiums
Property and casualty insurance premiums		(661)				(1,133)
Net investment and interest income	[8]	(373)		(401)		(1,157)		(1,214)
Other revenue	[8]	(132)		(131)		(395)		(392)
Total revenues		(2,383)		(1,604)		(5,898)		(4,487)
Costs and expenses:
Operating expenses	[7],[8]	(2,004)		(1,194)		(4,716)		(3,245)
Commission expenses
Cost of sales
Benefits and losses
Amortization of deferred policy acquisition costs
Lease expense	[8]	(83)		(47)		(183)		(140)
Depreciation, net of (gains) losses on disposals
Net gains on disposal of real estate
Total costs and expenses		(2,087)		(1,241)		(4,899)		(3,385)
Earnings (loss) from operations before equity in earnings of subsidiaries		(296)		(363)		(999)		(1,102)
Equity in earnings of subsidiaries	[9]	(11,823)		(9,046)		(25,998)		(25,925)
Earnings from operations		(12,119)		(9,409)		(26,997)		(27,027)
Interest expense	[8]	296		363		999		1,102
Amortization on early extinguishment of debt
Pretax earnings		(11,823)		(9,046)		(25,998)		(25,925)
Income tax expense
Earnings available to common shareholders		$ (11,823)		$ (9,046)		$ (25,998)		$ (25,925)

[1] Balances for the quarter ended September 30, 2017

[2] Balances for the quarter ended September 30, 2016

[3] Balances for the nine months ended September 30, 2017

[4] Balances for the nine months ended September 30, 2016

[5] Balance for the period ended September 30, 2017

[6] Balance for the period ended September 30, 2016

[7] Eliminate intercompany premiums

[8] Eliminate intercompany lease / interest income

[9] Eliminate equity in earnings of subsidiaries