Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Cash flow from operating activities:
Net earnings	$ 922,998	$ 1,123,286	$ 610,856
Earnings from consolidated subsidiaries	0	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	733,879	696,955	664,001
Amortization of deferred policy acquisition costs	27,924	33,854	28,293
Amortization of premiums and accretion of discounts related to investments, inc	20,066	19,749	14,229
Amortization of debt issuance costs	7,087	5,659	5,948
Interest credited to policyholders	55,822	64,692	55,321
Change in allowance for losses on trade receivables	(4,860)	4,227	1,206
Change in allowance for inventory reserves	9,490	15,235	1,298
Net gains on disposal of personal property	(247,084)	(214,203)	(54,071)
Net gains on disposal of real estate	5,596	(4,120)	3,281
Net gains on sales of investments	8,300	(11,872)	(10,058)
Net (gains) losses on equity investments	9,091	(7,837)	(394)
Deferred income taxes	131,754	101,091	68,411
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	44,714	(9,187)	(39,516)
Inventories and parts	(2,225)	(68,536)	(5,775)
Prepaid expenses	(5,575)	232,342	94,359
Capitalization of deferred policy acquisition costs	(25,202)	(32,626)	(36,162)
Other assets	16,027	15,349	44,251
Related party assets	(544)	(10,357)	(487)
Accounts payable and accrued expenses	34,263	10,514	78,718
Policy benefits and losses, claims and loss expenses payable	(13,708)	(19,692)	(1,992)
Other policyholders' funds and liabilities	(2,580)	(1,608)	2,230
Deferred income	5,137	5,399	11,388
Related party liabilities	(760)	(2,079)	60
Net cash provided by operating activities	1,729,610	1,946,235	1,535,395
Cash flow from investing activities:
Escrow deposits	9,298	(9,328)	(5,221)
Purchase of:
Property, plant and equipment	(2,723,901)	(2,136,537)	(1,441,475)
Short term investments	(60,037)	(74,418)	(69,929)
Fixed maturities investments	(563,452)	(627,326)	(606,233)
Equity Securities	(4,932)	(19,299)	(962)
Preferred stock	0	(8,000)	(16,144)
Real estate	(8,685)	(261)	(622)
Mortgage loans	(204,579)	(158,147)	(158,071)
Proceeds from sale and paydowns of:
Property, plant and equipment	701,331	623,235	537,484
Short term investments	74,457	51,591	69,718
Fixed maturities investments	196,635	360,937	529,239
Equity Securities	1,286	2,046	207
Preferred stock	0	2,000	2,700
Real estate	0	113	255
Mortgage loans	161,194	126,218	29,525
Net cash used by investing activities	(2,421,385)	(1,867,176)	(1,129,529)
Cash flow from financing activities:
Borrowings from credit facilities	1,017,898	1,969,474	922,008
Principal repayments on credit facilities	(801,994)	(437,506)	(662,588)
Debt issuance costs	(5,237)	(13,156)	(5,793)
Capital lease payments	(124,188)	(166,262)	(221,247)
Securitization deposits	217	0	0
Voting Common stock dividends paid	(19,608)	(29,412)	(49,019)
Series N Non-Voting Common Stock Dividends	(14,117)	0	0
Net contribution from (to) related party			0
Investment contract deposits	341,483	347,520	517,856
Investment contract withdrawals	(334,659)	(237,503)	(213,864)
Net cash provided by financing activities	59,795	1,433,155	287,353
Effects of exchange rate on cash	(11,633)	(2,089)	6,441
Increase (decrease) cash and cash equivalents	(643,613)	1,510,125	699,660
Cash and cash equivalents at beginning of period	2,704,137	1,194,012	494,352
Cash and cash equivalents at the end of period	2,060,524	2,704,137	1,194,012
Property and Casualty Insurance [Member]
Cash flow from financing activities:
Effects of exchange rate on cash	0
Increase (decrease) cash and cash equivalents	476
Cash and cash equivalents at beginning of period	10,800
Cash and cash equivalents at the end of period	11,276	10,800
Life Insurance [Member]
Cash flow from financing activities:
Effects of exchange rate on cash	0
Increase (decrease) cash and cash equivalents	(35,118)
Cash and cash equivalents at beginning of period	50,124
Cash and cash equivalents at the end of period	15,006	50,124
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	922,998	1,123,286	610,856
Earnings from consolidated subsidiaries	(39,727)	(54,746)	(44,441)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	733,879	696,955	664,001
Amortization of deferred policy acquisition costs	0	0	0
Amortization of premiums and accretion of discounts related to investments, inc	0	0	0
Amortization of debt issuance costs	7,087	5,659	5,948
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	(4,714)	4,689	1,424
Change in allowance for inventory reserves	9,490	15,235	1,298
Net gains on disposal of personal property	(247,084)	(214,203)	(54,071)
Net gains on disposal of real estate	5,596	(4,120)	3,281
Net gains on sales of investments	0	0	0
Net (gains) losses on equity investments	0	0	0
Deferred income taxes	137,159	106,869	72,407
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	39,510	(28,776)	(60,806)
Inventories and parts	(2,225)	(68,536)	(5,775)
Prepaid expenses	(5,575)	232,342	94,359
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	17,102	15,136	44,265
Related party assets	(4,898)	(10,517)	(12,790)
Accounts payable and accrued expenses	16,935	5,601	82,102
Policy benefits and losses, claims and loss expenses payable	5,849	(8,428)	14,919
Other policyholders' funds and liabilities	0	0	0
Deferred income	3,371	6,551	10,780
Related party liabilities	(1,048)	255	1,136
Net cash provided by operating activities	1,593,705	1,823,252	1,428,893
Cash flow from investing activities:
Escrow deposits	9,298	(9,328)	(5,221)
Purchase of:
Property, plant and equipment	(2,726,967)	(2,136,537)	(1,441,475)
Short term investments	0	0	0
Fixed maturities investments	(224,999)	0	0
Equity Securities	0	0	0
Preferred stock		0	0
Real estate	(2,677)	(33)	0
Mortgage loans	0	0	0
Proceeds from sale and paydowns of:
Property, plant and equipment	701,331	623,235	537,484
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity Securities	0	0	0
Preferred stock		0	0
Real estate	0	113	255
Mortgage loans	0	0	0
Net cash used by investing activities	(2,244,014)	(1,522,550)	(908,957)
Cash flow from financing activities:
Borrowings from credit facilities	1,017,898	1,969,474	912,408
Principal repayments on credit facilities	(801,994)	(426,319)	(652,728)
Debt issuance costs	(5,237)	(13,156)	(5,793)
Capital lease payments	(124,188)	(166,262)	(221,247)
Securitization deposits	217
Voting Common stock dividends paid	(19,608)	(29,412)	(49,019)
Series N Non-Voting Common Stock Dividends	(14,117)
Net contribution from (to) related party			41,199
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	52,971	1,334,325	24,820
Effects of exchange rate on cash	(11,633)	(2,089)	6,441
Increase (decrease) cash and cash equivalents	(608,971)	1,632,938	551,197
Cash and cash equivalents at beginning of period	2,643,213	1,010,275	459,078
Cash and cash equivalents at the end of period	2,034,242	2,643,213	1,010,275
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	29,755	39,402	25,720
Earnings from consolidated subsidiaries	0	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Amortization of premiums and accretion of discounts related to investments, inc	1,691	1,638	1,578
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	(146)	(456)	(217)
Change in allowance for inventory reserves	0	0	0
Net gains on disposal of personal property	0	0	0
Net gains on disposal of real estate	0	0	0
Net gains on sales of investments	44	(991)	(158)
Net (gains) losses on equity investments	9,091	(7,837)	(394)
Deferred income taxes	(2,757)	1,347	459
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	2,322	17,180	27,302
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	2	346	537
Related party assets	4,354	160	303
Accounts payable and accrued expenses	625	1,821	(3,497)
Policy benefits and losses, claims and loss expenses payable	(7,372)	(18,563)	(31,398)
Other policyholders' funds and liabilities	(819)	(177)	(2,053)
Deferred income	0	0	0
Related party liabilities	(640)	(2,644)	1,187
Net cash provided by operating activities	36,150	31,226	19,369
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	(59,425)	(74,418)	(69,929)
Fixed maturities investments	(41,391)	(10,248)	(18,823)
Equity Securities	(3,281)	(17,919)	0
Preferred stock		0	0
Real estate	(5,031)	(59)	0
Mortgage loans	(37,612)	(24,032)	(18,035)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	74,457	50,737	69,669
Fixed maturities investments	18,940	24,201	20,854
Equity Securities	1,280	20	0
Preferred stock		2,000	2,700
Real estate	0	0	0
Mortgage loans	16,389	23,634	17,659
Net cash used by investing activities	(35,674)	(26,084)	4,095
Cash flow from financing activities:
Borrowings from credit facilities	0	0	0
Principal repayments on credit facilities	0	0	0
Debt issuance costs	0	0	0
Capital lease payments	0	0	0
Securitization deposits	0
Voting Common stock dividends paid	0	0	0
Series N Non-Voting Common Stock Dividends	0
Net contribution from (to) related party			(22,600)
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	0	0	(22,600)
Effects of exchange rate on cash		0	0
Increase (decrease) cash and cash equivalents		5,142	864
Cash and cash equivalents at beginning of period	10,800	5,658	4,794
Cash and cash equivalents at the end of period		10,800	5,658
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	9,972	15,344	18,721
Earnings from consolidated subsidiaries	0	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0	0
Amortization of deferred policy acquisition costs	27,924	33,854	28,293
Amortization of premiums and accretion of discounts related to investments, inc	18,375	18,111	12,651
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	55,822	64,692	55,321
Change in allowance for losses on trade receivables	0	(6)	(1)
Change in allowance for inventory reserves	0	0	0
Net gains on disposal of personal property	0	0	0
Net gains on disposal of real estate	0	0	0
Net gains on sales of investments	8,256	(10,881)	(9,900)
Net (gains) losses on equity investments	0	0	0
Deferred income taxes	(2,648)	(7,125)	(4,455)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	2,882	2,409	(6,012)
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	(25,202)	(32,626)	(36,162)
Other assets	(1,077)	(133)	(551)
Related party assets	0	0	0
Accounts payable and accrued expenses	16,703	3,092	113
Policy benefits and losses, claims and loss expenses payable	(12,185)	7,299	14,487
Other policyholders' funds and liabilities	(1,761)	(1,431)	4,283
Deferred income	1,766	(1,152)	608
Related party liabilities	928	310	9,737
Net cash provided by operating activities	99,755	91,757	87,133
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	(612)	0	0
Fixed maturities investments	(297,062)	(617,078)	(587,410)
Equity Securities	(1,651)	(1,380)	(962)
Preferred stock		(8,000)	(16,144)
Real estate	(977)	(169)	(622)
Mortgage loans	(166,967)	(134,115)	(140,036)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	0	854	49
Fixed maturities investments	177,695	336,736	508,385
Equity Securities	6	2,026	207
Preferred stock		0	0
Real estate	3,066	0	0
Mortgage loans	144,805	102,584	11,866
Net cash used by investing activities	(141,697)	(318,542)	(224,667)
Cash flow from financing activities:
Borrowings from credit facilities	0	0	9,600
Principal repayments on credit facilities	0	(11,187)	(9,860)
Debt issuance costs	0	0	0
Capital lease payments	0	0	0
Securitization deposits	0
Voting Common stock dividends paid	0	0	0
Series N Non-Voting Common Stock Dividends	0
Net contribution from (to) related party			(18,599)
Investment contract deposits	341,483	347,520	517,856
Investment contract withdrawals	(334,659)	(237,503)	(213,864)
Net cash provided by financing activities	6,824	98,830	285,133
Effects of exchange rate on cash		0	0
Increase (decrease) cash and cash equivalents		(127,955)	147,599
Cash and cash equivalents at beginning of period	50,124	178,079	30,480
Cash and cash equivalents at the end of period		50,124	178,079
Eliminations [Member]
Cash flow from operating activities:
Net earnings	(39,727)	(54,746)	(44,441)
Earnings from consolidated subsidiaries	39,727	54,746	44,441
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Amortization of premiums and accretion of discounts related to investments, inc	0	0	0
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	0	0	0
Change in allowance for inventory reserves	0	0	0
Net gains on disposal of personal property	0	0	0
Net gains on disposal of real estate	0	0	0
Net gains on sales of investments	0	0	0
Net (gains) losses on equity investments	0	0	0
Deferred income taxes	0	0	0
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	0	0	0
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	0	0	0
Related party assets	0	0	12,000
Accounts payable and accrued expenses	0	0	0
Policy benefits and losses, claims and loss expenses payable	0	0	0
Other policyholders' funds and liabilities	0	0	0
Deferred income	0	0	0
Related party liabilities	0	0	(12,000)
Net cash provided by operating activities	0	0	0
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	3,066	0	0
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity Securities	0	0	0
Preferred stock		0	0
Real estate	0	0	0
Mortgage loans	0	0	0
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity Securities	0	0	0
Preferred stock		0	0
Real estate	(3,066)	0	0
Mortgage loans	0	0	0
Net cash used by investing activities	0	0	0
Cash flow from financing activities:
Borrowings from credit facilities	0	0	0
Principal repayments on credit facilities	0	0	0
Debt issuance costs	0	0	0
Capital lease payments	0	0	0
Securitization deposits	0
Voting Common stock dividends paid	0	0	0
Series N Non-Voting Common Stock Dividends	0
Net contribution from (to) related party			0
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	0	0	0
Effects of exchange rate on cash	0	0	0
Increase (decrease) cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at the end of period	$ 0	$ 0	$ 0