Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2018		Mar. 31, 2017		Mar. 31, 2016
Cash flow from operating activities:
Net earnings		$ 790,583		$ 398,424		$ 489,001
Earnings from consolidated subsidiaries
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation		555,069		481,520		389,393
Amortization of deferred policy acquisition costs		24,514		26,218		23,272
Amortization of debt issuance costs		3,868		4,062		3,419
Interest credited to policyholders		32,302		25,020		20,465
Change in allowance for losses on trade receivables		(120)		(46)		(205)
Change in allowance for inventory reserves		5,065		1,330		(1,343)
Net gains on disposal of personal property		(11,822)		(32,495)		(98,158)
Net gains on disposal of real estate		(195,414)		(3,590)		(545)
Net gains on sales of investments		(6,269)		(5,284)		(4,491)
Deferred income taxes		(193,434)		173,112		138,075
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables		(15,329)		(2,890)		14,765
Inventories and parts		(12,384)		(4,072)		(9,009)
Prepaid expenses		(40,765)		9,386		(10,338)
Capitalization of deferred policy acquisition costs		(27,350)		(27,111)		(32,590)
Other assets		(165,968)		(2,488)		16,261
Related party assets		53,408		343		56,644
Accounts payable and accrued expenses		(25,546)		(5,056)		37,312
Policy benefits and losses, claims and loss expenses payable		161,121		15,378		9,626
Other policyholders' funds and liabilities		(109)		1,499		(349)
Deferred income		5,524		5,921		4,757
Related party liabilities		(616)		(1,062)		(616)
Net cash provided by operating activities		936,328		1,058,119		1,045,346
Cash flow from investing activities:
Escrow deposits		31,362		(38,058)		(4,358)
Purchase of:
Property, plant and equipment		(1,363,745)		(1,419,505)		(1,509,154)
Short term investments		(63,556)		(635,847)		(515,899)
Fixed maturities investments		(390,900)		(355,101)		(398,987)
Equity securities		(662)		(489)		(1,315)
Preferred stock		(1,000)				(1,005)
Real estate		(1,939)		(32,807)		(15,459)
Mortgage loans		(83,507)		(154,310)		(87,204)
Proceeds from sale and paydowns of:
Property, plant and equipment		699,803		487,475		539,256
Short term investments		67,790		655,726		528,180
Fixed maturities investments		164,825		190,578		154,536
Equity securities						2,044
Preferred stock		4,208		4,181		1,126
Real estate		2,783		8,753		21,589
Mortgage loans		37,590		106,832		26,968
Net cash used by investing activities		(896,948)		(1,182,572)		(1,259,682)
Cash flow from financing activities:
Borrowings from credit facilities		498,464		742,625		837,972
Principal repayments on credit facilities		(356,451)		(367,844)		(428,403)
Debt issuance costs		(5,111)		(5,055)		(10,184)
Capital lease payments		(296,363)		(212,545)		(168,661)
Employee stock ownership plan		(11,640)		(11,106)		(9,302)
Securitization deposits		(2,180)		446		544
Common stock dividends paid		(29,380)		(58,757)		(78,374)
Investment contract deposits		401,814		285,148		358,237
Investment contract withdrawals		(182,549)		(149,159)		(112,957)
Net cash provided by financing activities		16,604		223,753		388,872
Effects of exchange rate on cash		5,598		(2,140)		(15,740)
Increase (decrease) in cash and cash equivalents		61,582		97,160		158,796
Cash and cash equivalents at the beginning of period		697,806		600,646		441,850
Cash and cash equivalents at the end of the period		759,388		697,806		600,646
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings		790,583		398,424		489,001
Earnings from consolidated subsidiaries		(46,990)		(35,797)		(35,522)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation		555,069		481,520		389,393
Amortization of deferred policy acquisition costs
Amortization of debt issuance costs		3,868		4,062		3,419
Interest credited to policyholders
Change in allowance for losses on trade receivables		(31)		31		7
Change in allowance for inventory reserves		5,065		1,330		(1,343)
Net gains on disposal of personal property		(11,822)		(32,495)		(98,158)
Net gains on disposal of real estate		(195,414)		(3,590)		(545)
Net gains on sales of investments
Deferred income taxes		(182,358)		173,059		124,838
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables		(23,444)		(6,806)		(2,169)
Inventories and parts		(12,384)		(4,072)		(9,009)
Prepaid expenses		(40,765)		9,386		(10,338)
Capitalization of deferred policy acquisition costs
Other assets		(167,579)		(3,827)		17,170
Related party assets		48,855		(872)		55,962
Accounts payable and accrued expenses		(36,384)		(14,793)		26,018
Policy benefits and losses, claims and loss expenses payable		168,687		13,283		23,215
Other policyholders' funds and liabilities
Deferred income		5,524		5,921		4,757
Related party liabilities		(1,884)		(1,170)		17,296
Net cash provided by operating activities		858,596		983,594		993,992
Cash flow from investing activities:
Escrow deposits		31,362		(38,058)		(4,358)
Purchase of:
Property, plant and equipment		(1,363,745)		(1,419,505)		(1,509,154)
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate		(1,365)		(19,406)		(15,384)
Mortgage loans
Proceeds from sale and paydowns of:
Property, plant and equipment		699,803		487,475		539,256
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate		2,783		6,275		21,589
Mortgage loans
Net cash used by investing activities		(631,162)		(983,219)		(968,051)
Cash flow from financing activities:
Borrowings from credit facilities		498,464		715,625		790,972
Principal repayments on credit facilities		(356,451)		(340,844)		(381,403)
Debt issuance costs		(5,111)		(5,055)		(10,184)
Capital lease payments		(296,363)		(212,545)		(168,661)
Employee stock ownership plan		(11,640)		(11,106)		(9,302)
Securitization deposits		(2,180)		446		544
Common stock dividends paid		(29,380)		(58,757)		(78,374)
Investment contract deposits
Investment contract withdrawals
Net cash provided by financing activities		(202,661)		87,764		143,592
Effects of exchange rate on cash		5,598		(2,140)		(15,740)
Increase (decrease) in cash and cash equivalents		30,371		85,999		153,793
Cash and cash equivalents at the beginning of period		671,665		585,666		431,873
Cash and cash equivalents at the end of the period		702,036		671,665		585,666
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings		22,889	[1]	17,815	[2]	16,168	[3]
Earnings from consolidated subsidiaries			[4]		[5]		[6]
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			[4]		[5]		[6]
Amortization of deferred policy acquisition costs			[1]		[2]		[3]
Amortization of debt issuance costs
Interest credited to policyholders
Change in allowance for losses on trade receivables			[4]		[5]		[6]
Change in allowance for inventory reserves			[4]		[5]		[6]
Net gains on disposal of personal property			[4]		[5]		[6]
Net gains on disposal of real estate
Net gains on sales of investments		(1,703)	[4]	(2,636)	[5]	(1,317)	[6]
Deferred income taxes		(6,596)	[4]	2,340	[5]	9,311	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables		8,075	[4]	4,221	[5]	13,528	[6]
Inventories and parts			[4]		[5]		[6]
Prepaid expenses			[4]		[5]		[6]
Capitalization of deferred policy acquisition costs			[4]		[5]		[6]
Other assets		1,810	[4]	1,341	[5]	(1,050)	[6]
Related party assets		4,553	[4]	1,215	[5]	682	[6]
Accounts payable and accrued expenses		648	[4]	392	[5]	1,533	[6]
Policy benefits and losses, claims and loss expenses payable		(10,623)	[4]	(7,838)	[5]	(18,925)	[6]
Other policyholders' funds and liabilities		1,194	[4]	1,167	[5]	(1,056)	[6]
Deferred income			[4]		[5]		[6]
Related party liabilities		318	[4]	226	[5]	115	[6]
Net cash provided by operating activities		20,565	[4]	18,243	[5]	18,989	[6]
Cash flow from investing activities:
Escrow deposits
Purchase of:
Property, plant and equipment			[4]		[5]		[6]
Short term investments		(63,556)	[4]	(77,693)	[5]	(44,735)	[6]
Fixed maturities investments		(51,273)	[4]	(42,628)	[5]	(45,048)	[6]
Equity securities			[4]		[5]		[6]
Preferred stock		(1,000)				(1,005)	[6]
Real estate		(440)	[4]	(4,648)	[5]	(36)	[6]
Mortgage loans		(14,409)	[4]	(21,021)	[5]	(1,800)	[6]
Proceeds from sale and paydowns of:
Property, plant and equipment			[4]		[5]		[6]
Short term investments		61,133	[4]	80,225	[5]	44,756	[6]
Fixed maturities investments		23,026	[4]	32,127	[5]	26,193	[6]
Equity securities	[6]					1,236
Preferred stock		4,208		4,181	[5]	1,126	[6]
Real estate			[4]				[6]
Mortgage loans		15,660	[4]	9,890	[5]	5,878	[6]
Net cash used by investing activities		(26,651)	[4]	(19,567)	[5]	(13,435)	[6]
Cash flow from financing activities:
Borrowings from credit facilities			[4]		[5]		[6]
Principal repayments on credit facilities			[4]		[5]		[6]
Debt issuance costs			[4]		[5]		[6]
Capital lease payments			[4]		[5]		[6]
Employee stock ownership plan			[4]		[5]		[6]
Securitization deposits			[4]
Common stock dividends paid			[4]		[5]
Investment contract deposits			[4]		[5]		[6]
Investment contract withdrawals			[4]		[5]		[6]
Net cash provided by financing activities			[4]		[5]		[6]
Effects of exchange rate on cash			[4]		[5]		[6]
Increase (decrease) in cash and cash equivalents		(6,086)	[4]	(1,324)	[5]	5,554	[6]
Cash and cash equivalents at the beginning of period		12,725	[7]	14,049	[6]	8,495	[6]
Cash and cash equivalents at the end of the period		6,639	[8]	12,725	[7]	14,049	[6]
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings		24,101	[1]	17,982	[2]	19,354	[3]
Earnings from consolidated subsidiaries			[4]		[5]		[6]
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			[4]		[5]		[6]
Amortization of deferred policy acquisition costs		24,514	[1]	26,218	[2]	23,272	[3]
Amortization of debt issuance costs
Interest credited to policyholders		32,302		25,020		20,465
Change in allowance for losses on trade receivables		(89)	[4]	(77)	[5]	(212)	[6]
Change in allowance for inventory reserves			[4]		[5]		[6]
Net gains on disposal of personal property			[4]		[5]		[6]
Net gains on disposal of real estate
Net gains on sales of investments		(4,566)	[4]	(2,648)	[5]	(3,174)	[6]
Deferred income taxes		(4,480)	[4]	(2,287)	[5]	3,926	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables		40	[4]	(305)	[5]	3,406	[6]
Inventories and parts			[4]		[5]		[6]
Prepaid expenses			[4]		[5]		[6]
Capitalization of deferred policy acquisition costs		(27,350)	[4]	(27,111)	[5]	(32,590)	[6]
Other assets		(199)	[4]	(2)	[5]	141	[6]
Related party assets			[4]		[5]	(18,075)	[6]
Accounts payable and accrued expenses		10,190	[4]	9,345	[5]	9,761	[6]
Policy benefits and losses, claims and loss expenses payable		3,057	[4]	9,933	[5]	5,336	[6]
Other policyholders' funds and liabilities		(1,303)	[4]	332	[5]	707	[6]
Deferred income			[4]		[5]		[6]
Related party liabilities		950	[4]	(118)	[5]	48	[6]
Net cash provided by operating activities		57,167	[4]	56,282	[5]	32,365	[6]
Cash flow from investing activities:
Escrow deposits
Purchase of:
Property, plant and equipment			[4]		[5]		[6]
Short term investments			[4]	(558,154)	[5]	(471,164)	[6]
Fixed maturities investments		(339,627)	[4]	(312,473)	[5]	(353,939)	[6]
Equity securities		(662)	[4]	(489)	[5]	(1,315)	[6]
Preferred stock							[6]
Real estate		(134)	[4]	(8,753)	[5]	(39)	[6]
Mortgage loans		(69,098)	[4]	(133,289)	[5]	(85,404)	[6]
Proceeds from sale and paydowns of:
Property, plant and equipment			[4]		[5]		[6]
Short term investments		6,657	[4]	575,501	[5]	483,424	[6]
Fixed maturities investments		141,799	[4]	158,451	[5]	128,343	[6]
Equity securities	[6]					808
Preferred stock					[5]		[6]
Real estate			[4]	2,478			[6]
Mortgage loans		21,930	[4]	96,942	[5]	21,090	[6]
Net cash used by investing activities		(239,135)	[4]	(179,786)	[5]	(278,196)	[6]
Cash flow from financing activities:
Borrowings from credit facilities			[4]	27,000	[5]	47,000	[6]
Principal repayments on credit facilities			[4]	(27,000)	[5]	(47,000)	[6]
Debt issuance costs			[4]		[5]		[6]
Capital lease payments			[4]		[5]		[6]
Employee stock ownership plan			[4]		[5]		[6]
Securitization deposits			[4]
Common stock dividends paid			[4]		[5]
Investment contract deposits		401,814	[4]	285,148	[5]	358,237	[6]
Investment contract withdrawals		(182,549)	[4]	(149,159)	[5]	(112,957)	[6]
Net cash provided by financing activities		219,265	[4]	135,989	[5]	245,280	[6]
Effects of exchange rate on cash			[4]		[5]		[6]
Increase (decrease) in cash and cash equivalents		37,297	[4]	12,485	[5]	(551)	[6]
Cash and cash equivalents at the beginning of period		13,416	[7]	931	[6]	1,482	[6]
Cash and cash equivalents at the end of the period		50,713	[8]	13,416	[7]	931	[6]
Eliminations [Member]
Cash flow from operating activities:
Net earnings		(46,990)		(35,797)		(35,522)
Earnings from consolidated subsidiaries		46,990		35,797		35,522
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation
Amortization of deferred policy acquisition costs
Amortization of debt issuance costs
Interest credited to policyholders
Change in allowance for losses on trade receivables
Change in allowance for inventory reserves
Net gains on disposal of personal property
Net gains on disposal of real estate
Net gains on sales of investments
Deferred income taxes
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables
Inventories and parts
Prepaid expenses
Capitalization of deferred policy acquisition costs
Other assets
Related party assets					[9]	18,075	[9]
Accounts payable and accrued expenses
Policy benefits and losses, claims and loss expenses payable
Other policyholders' funds and liabilities
Deferred income
Related party liabilities					[9]	(18,075)	[9]
Net cash provided by operating activities
Cash flow from investing activities:
Escrow deposits
Purchase of:
Property, plant and equipment
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate
Mortgage loans							[9]
Proceeds from sale and paydowns of:
Property, plant and equipment
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate
Mortgage loans							[9]
Net cash used by investing activities
Cash flow from financing activities:
Borrowings from credit facilities
Principal repayments on credit facilities
Debt issuance costs
Capital lease payments
Employee stock ownership plan
Securitization deposits
Common stock dividends paid
Investment contract deposits
Investment contract withdrawals
Net cash provided by financing activities
Effects of exchange rate on cash
Increase (decrease) in cash and cash equivalents
Cash and cash equivalents at the beginning of period
Cash and cash equivalents at the end of the period

[1] Balances for the year ended December 31, 2016

[2] Balances for the year ended December 31, 2015

[3] Balances for the year ended December 31, 2014

[4] Balance for the period ended December 31, 2016

[5] Balance for the period ended December 31, 2015

[6] Balance for the period ended December 31, 2014

[7] Balances as of December 31, 2015

[8] Balances as of December 31, 2016

[9] Eliminate intercompany investments