Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019		Mar. 31, 2018		Mar. 31, 2017
Cash flow from operating activities:
Net earnings	$ 370,857		$ 790,583		$ 398,424
Earnings from consolidated subsidiaries
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	581,025		555,069		481,520
Amortization of deferred policy acquisition costs	28,556		24,514		26,218
Amortization of premiums and accretion of discounts related to investments, net	13,107		12,790		11,828
Amortization of debt issuance costs	3,923		3,868		4,062
Interest credited to policyholders	35,387		32,302		25,020
Change in allowance for losses on trade receivables	52		(120)		(46)
Change in allowance for inventory reserves	(146)		5,065		1,330
Net gains on disposal of personal property	(26,982)		(11,822)		(32,495)
Net gains on disposal of real estate	(44)		(195,414)		(3,590)
Net gains on sales of investments	(2,663)		(6,269)		(5,284)
Net losses on equity investments	5,739
Deferred income taxes	106,811		(193,434)		173,112
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(31,365)		(15,329)		(2,890)
Inventories and parts	(13,492)		(12,384)		(4,072)
Prepaid expenses	(8,620)		(40,765)		9,386
Capitalization of deferred policy acquisition costs	(25,957)		(27,350)		(27,111)
Other assets	157,152		(165,968)		(2,488)
Related party assets	4,194		53,408		343
Accounts payable and accrued expenses	10,263		(36,980)		(15,548)
Policy benefits and losses, claims and loss expenses payable	(236,120)		161,121		15,378
Other policyholders' funds and liabilities	5,007		(109)		1,499
Deferred income	966		5,524		5,921
Related party liabilities	(2,067)		(616)		(1,062)
Net cash provided by operating activities	975,583		937,684		1,059,455
Cash flow from investing activities:
Escrow deposits	4,299		31,362		(38,058)
Purchase of:
Property, plant and equipment	(1,869,968)		(1,363,745)		(1,419,505)
Short term investments	(54,048)		(63,556)		(635,847)
Fixed maturities investments	(540,045)		(390,900)		(355,101)
Equity securities	(957)		(662)		(489)
Preferred stock			(1,000)
Real estate	(635)		(1,939)		(32,807)
Mortgage loans	(63,611)		(83,507)		(154,310)
Proceeds from sale and paydowns of:
Property, plant and equipment	606,271		699,803		487,475
Short term investments	66,037		67,790		655,726
Fixed maturities investments	123,551		163,469		189,242
Equity securities	8,608
Preferred stock	1,625		4,208		4,181
Real estate			2,783		8,753
Mortgage loans	147,737		37,590		106,832
Net cash used by investing activities	(1,571,136)		(898,304)		(1,183,908)
Cash flow from financing activities:
Borrowings from credit facilities	897,311		498,464		742,625
Principal repayments on credit facilities	(299,748)		(356,451)		(367,844)
Debt issuance costs	(7,243)		(5,111)		(5,055)
Capital lease payments	(303,431)		(296,363)		(212,545)
Employee stock ownership plan	(418)		(11,640)		(11,106)
Securitization deposits			(2,180)		446
Common stock dividends paid	(39,179)		(29,380)		(58,757)
Investment contract deposits	400,123		401,814		285,148
Investment contract withdrawals	(132,833)		(182,549)		(149,159)
Net cash provided by financing activities	514,582		16,604		223,753
Effects of exchange rate on cash	(4,716)		5,598		(2,140)
Increase (decrease) in cash and cash equivalents	(85,687)		61,582		97,160
Cash and cash equivalents at the beginning of period	759,388		697,806		600,646
Cash and cash equivalents at the end of the period	673,701		759,388		697,806
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	370,857		790,583		398,424
Earnings from consolidated subsidiaries	(41,811)		(46,990)		(35,797)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	581,025		555,069		481,520
Amortization of deferred policy acquisition costs
Amortization of premiums and accretion of discounts related to investments, net
Amortization of debt issuance costs	3,923		3,868		4,062
Interest credited to policyholders
Change in allowance for losses on trade receivables	57		(31)		31
Change in allowance for inventory reserves	(146)		5,065		1,330
Net gains on disposal of personal property	(26,982)		(11,822)		(32,495)
Net gains on disposal of real estate	(44)		(195,414)		(3,590)
Net gains on sales of investments
Net losses on equity investments
Deferred income taxes	112,434		(182,358)		173,059
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(26,160)		(23,444)		(6,806)
Inventories and parts	(13,492)		(12,384)		(4,072)
Prepaid expenses	(8,620)		(40,765)		9,386
Capitalization of deferred policy acquisition costs
Other assets	159,126		(167,579)		(3,827)
Related party assets	3,857		48,855		(872)
Accounts payable and accrued expenses	6,454		(36,384)		(14,793)
Policy benefits and losses, claims and loss expenses payable	(159,793)		168,687		13,283
Other policyholders' funds and liabilities
Deferred income	966		5,524		5,921
Related party liabilities	(2,711)		(1,884)		(1,170)
Net cash provided by operating activities	958,940		858,596		983,594
Cash flow from investing activities:
Escrow deposits	4,299		31,362		(38,058)
Purchase of:
Property, plant and equipment	(1,869,968)		(1,363,745)		(1,419,505)
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate	(236)		(1,365)		(19,406)
Mortgage loans
Proceeds from sale and paydowns of:
Property, plant and equipment	606,271		699,803		487,475
Short term investments
Fixed maturities investments
Equity securities
Preferred stock
Real estate			2,783		6,275
Mortgage loans
Net cash used by investing activities	(1,259,634)		(631,162)		(983,219)
Cash flow from financing activities:
Borrowings from credit facilities	897,311		498,464		715,625
Principal repayments on credit facilities	(299,748)		(356,451)		(340,844)
Debt issuance costs	(7,243)		(5,111)		(5,055)
Capital lease payments	(303,431)		(296,363)		(212,545)
Employee stock ownership plan	(418)		(11,640)		(11,106)
Securitization deposits			(2,180)		446
Common stock dividends paid	(39,179)		(29,380)		(58,757)
Investment contract deposits
Investment contract withdrawals
Net cash provided by financing activities	247,292		(202,661)		87,764
Effects of exchange rate on cash	(4,716)		5,598		(2,140)
Increase (decrease) in cash and cash equivalents	(58,118)		30,371		85,999
Cash and cash equivalents at the beginning of period	702,036		671,665		585,666
Cash and cash equivalents at the end of the period	643,918		702,036		671,665
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	21,708	[1]	22,889	[2]	17,815	[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 premiums and accretion of discounts related to investments, net	1,361	[4]	1,356	[5]	1,336	[6]
Amortization of debt issuance costs		[4]		[5]		[6]
Interest credited to policyholders		[4]		[5]		[6]
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		[1]		[2]		[3]
Net gains on sales of investments	(2,971)	[4]	(1,703)	[5]	(2,636)	[6]
Net losses on equity investments	5,739	[4]		[5]		[6]
Deferred income taxes	830	[4]	(6,596)	[5]	2,340	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(2,438)	[4]	8,075	[5]	4,221	[6]
Inventories and parts		[4]		[5]		[6]
Prepaid expenses		[4]		[5]		[6]
Capitalization of deferred policy acquisition costs		[4]		[5]		[6]
Other assets	(1,449)	[4]	1,810	[5]	1,341	[6]
Related party assets	339	[4]	4,553	[5]	1,215	[6]
Accounts payable and accrued expenses	257	[4]	648	[5]	392	[6]
Policy benefits and losses, claims and loss expenses payable	(4,400)	[4]	(10,623)	[5]	(7,838)	[6]
Other policyholders' funds and liabilities	(117)	[4]	1,194	[5]	1,167	[6]
Deferred income		[4]		[5]		[6]
Related party liabilities	944	[4]	318	[5]	226	[6]
Net cash provided by operating activities	19,803	[4]	21,921	[5]	19,579	[6]
Cash flow from investing activities:
Escrow deposits		[4]		[5]		[6]
Purchase of:
Property, plant and equipment		[4]		[5]		[6]
Short term investments	(53,878)	[4]	(63,556)	[5]	(77,693)	[6]
Fixed maturities investments	(33,775)	[4]	(51,273)	[5]	(42,628)	[6]
Equity securities		[4]		[5]		[6]
Preferred stock		[4]	(1,000)	[5]		[6]
Real estate	(187)	[4]	(440)	[5]	(4,648)	[6]
Mortgage loans	(20,031)	[4]	(14,409)	[5]	(21,021)	[6]
Proceeds from sale and paydowns of:
Property, plant and equipment		[4]		[5]		[6]
Short term investments	58,767	[4]	61,133	[5]	80,225	[6]
Fixed maturities investments	12,305	[4]	21,670	[5]	30,791	[6]
Equity securities	8,608	[4]				[6]
Preferred stock	1,625	[4]	4,208	[5]	4,181	[6]
Real estate		[4]		[5]		[6]
Mortgage loans	5,881	[4]	15,660	[5]	9,890	[6]
Net cash used by investing activities	(20,685)	[4]	(28,007)	[5]	(20,903)	[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]		[5]		[6]
Common stock dividends paid		[4]		[5]		[6]
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	(882)	[4]	(6,086)	[5]	(1,324)	[6]
Cash and cash equivalents at the beginning of period	6,639	[7]	12,725	[6]	14,049	[6]
Cash and cash equivalents at the end of the period	5,757	[8]	6,639	[7]	12,725	[6]
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	20,103	[1]	24,101	[2]	17,982	[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	28,556	[1]	24,514	[2]	26,218	[3]
Amortization of premiums and accretion of discounts related to investments, net	11,746	[4]	11,434	[5]	10,492	[6]
Amortization of debt issuance costs		[4]		[5]		[6]
Interest credited to policyholders	35,387	[4]	32,302	[5]	25,020	[6]
Change in allowance for losses on trade receivables	(5)	[4]	(89)	[5]	(77)	[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		[1]		[2]		[3]
Net gains on sales of investments	308	[4]	(4,566)	[5]	(2,648)	[6]
Net losses on equity investments		[4]		[5]		[6]
Deferred income taxes	(6,453)	[4]	(4,480)	[5]	(2,287)	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(2,767)	[4]	40	[5]	(305)	[6]
Inventories and parts		[4]		[5]		[6]
Prepaid expenses		[4]		[5]		[6]
Capitalization of deferred policy acquisition costs	(25,957)	[4]	(27,350)	[5]	(27,111)	[6]
Other assets	(525)	[4]	(199)	[5]	(2)	[6]
Related party assets	(2)	[4]		[5]	0	[6]
Accounts payable and accrued expenses	3,552	[4]	(1,244)	[5]	(1,147)	[6]
Policy benefits and losses, claims and loss expenses payable	(71,927)	[4]	3,057	[5]	9,933	[6]
Other policyholders' funds and liabilities	5,124	[4]	(1,303)	[5]	332	[6]
Deferred income		[4]		[5]		[6]
Related party liabilities	(300)	[4]	950	[5]	(118)	[6]
Net cash provided by operating activities	(3,160)	[4]	57,167	[5]	56,282	[6]
Cash flow from investing activities:
Escrow deposits		[4]		[5]		[6]
Purchase of:
Property, plant and equipment		[4]		[5]		[6]
Short term investments	(170)	[4]		[5]	(558,154)	[6]
Fixed maturities investments	(506,270)	[4]	(339,627)	[5]	(312,473)	[6]
Equity securities	(957)	[4]	(662)	[5]	(489)	[6]
Preferred stock		[4]		[5]		[6]
Real estate	(212)	[4]	(134)	[5]	(8,753)	[6]
Mortgage loans	(43,580)	[4]	(69,098)	[5]	(133,289)	[6]
Proceeds from sale and paydowns of:
Property, plant and equipment		[4]		[5]		[6]
Short term investments	7,270	[4]	6,657	[5]	575,501	[6]
Fixed maturities investments	111,246	[4]	141,799	[5]	158,451	[6]
Equity securities		[4]				[6]
Preferred stock		[4]		[5]		[6]
Real estate		[4]		[5]	2,478	[6]
Mortgage loans	141,856	[4]	21,930	[5]	96,942	[6]
Net cash used by investing activities	(290,817)	[4]	(239,135)	[5]	(179,786)	[6]
Cash flow from financing activities:
Borrowings from credit facilities		[4]		[5]	27,000	[6]
Principal repayments on credit facilities		[4]		[5]	(27,000)	[6]
Debt issuance costs		[4]		[5]		[6]
Capital lease payments		[4]		[5]		[6]
Employee stock ownership plan		[4]		[5]		[6]
Securitization deposits		[4]		[5]		[6]
Common stock dividends paid		[4]		[5]		[6]
Investment contract deposits	400,123	[4]	401,814	[5]	285,148	[6]
Investment contract withdrawals	(132,833)	[4]	(182,549)	[5]	(149,159)	[6]
Net cash provided by financing activities	267,290	[4]	219,265	[5]	135,989	[6]
Effects of exchange rate on cash		[4]		[5]		[6]
Increase (decrease) in cash and cash equivalents	(26,687)	[4]	37,297	[5]	12,485	[6]
Cash and cash equivalents at the beginning of period	50,713	[7]	13,416	[6]	931	[6]
Cash and cash equivalents at the end of the period	24,026	[8]	50,713	[7]	13,416	[6]
Eliminations [Member]
Cash flow from operating activities:
Net earnings	(41,811)		(46,990)		(35,797)
Earnings from consolidated subsidiaries	41,811		46,990		35,797
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation
Amortization of deferred policy acquisition costs
Amortization of premiums and accretion of discounts related to investments, net
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
Net losses on equity 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]		[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]		[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, 2018

[5] Balance for the period ended December 31, 2017

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

[7] Balances as of December 31, 2016

[8] Balances as of December 31, 2018

[9] Eliminate intercompany investments