Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Cash flow from operating activities:
Net earnings	$ 610,856	$ 442,048	$ 370,857
Earnings from consolidated subsidiaries	0	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	664,001	664,120	581,025
Amortization of deferred policy acquisition costs	28,293	31,219	28,556
Amortization of premiums and accretion of discounts related to investments, net	14,229	13,317	13,107
Amortization of debt issuance costs	5,948	4,426	3,923
Interest credited to policyholders	55,321	51,857	35,387
Change in allowance for losses on trade receivables	1,206	(14)	52
Change in allowance for inventory reserves	1,298	640	(146)
Net gains on disposal of personal property	(54,071)	(27,057)	(26,982)
Net gains on disposal of real estate	3,281	(758)	(44)
Net gains on sales of investments	(10,058)	(13,596)	(2,663)
Net losses on equity investments	(394)	(3,783)	5,739
Deferred income taxes	68,411	317,893	106,811
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(39,516)	38,129	(31,365)
Inventories and parts	(5,775)	1,776	(13,492)
Prepaid expenses	94,359	(391,120)	(8,620)
Capitalization of deferred policy acquisition costs	(36,162)	(24,447)	(25,957)
Other assets	29,865	(1,295)	157,152
Related party assets	(487)	(5,645)	4,194
Accounts payable and accrued expenses	92,925	(4,530)	10,263
Policy benefits and losses, claims and loss expenses payable	(1,992)	(12,618)	(236,120)
Other policyholders' funds and liabilities	2,230	(4,857)	5,007
Deferred income	11,567	(1,818)	966
Related party liabilities	60	1,626	(2,067)
Net cash provided by operating activities	1,535,395	1,075,513	975,583
Cash flow from investing activities:
Escrow deposits	(5,221)	6,617	4,299
Purchase of:
Property, plant and equipment	(1,441,475)	(2,309,406)	(1,869,968)
Short term investments	(69,929)	(61,226)	(54,048)
Fixed maturities investments	(606,233)	(379,349)	(540,045)
Equity securities	(962)	(83)	(957)
Preferred stock	(16,144)	0	0
Real estate	(622)	(4,286)	(635)
Mortgage loans	(158,071)	(62,016)	(63,611)
Proceeds from sale and paydowns of:
Property, plant and equipment	537,484	687,375	606,271
Short term investments	69,718	59,056	66,037
Fixed maturities investments	529,239	268,636	123,551
Equity securities	207	185	8,608
Preferred stock	2,700	2,375	1,625
Real estate	255	311	0
Mortgage loans	29,525	25,162	147,737
Net cash used by investing activities	(1,129,529)	(1,766,649)	(1,571,136)
Cash flow from financing activities:
Borrowings from credit facilities	922,008	1,121,412	897,311
Principal repayments on credit facilities	(662,588)	(349,986)	(299,748)
Debt issuance costs	(5,793)	(5,332)	(7,243)
Capital lease payments	(221,247)	(307,782)	(303,431)
Employee stock ownership plan shares	0	(206)	(418)
Common stock dividends paid	(49,019)	(29,404)	(39,179)
Net contribution from (to) related party	0	0
Investment contract deposits	517,856	234,640	400,123
Investment contract withdrawals	(213,864)	(151,022)	(132,833)
Net cash provided by financing activities	287,353	512,320	514,582
Effects of exchange rate on cash	6,441	(533)	(4,716)
Increase (decrease) in cash and cash equivalents	699,660	(179,349)	(85,687)
Cash and cash equivalents at the beginning of period	494,352	673,701	759,388
Cash and cash equivalents at the end of the period	1,194,012	494,352	673,701
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	610,856	442,048	370,857
Earnings from consolidated subsidiaries	(44,441)	(55,789)	(41,811)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	664,001	664,120	581,025
Amortization of deferred policy acquisition costs	0	0	0
Amortization of premiums and accretion of discounts related to investments, net	0	0	0
Amortization of debt issuance costs	5,948	4,426	3,923
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	1,424	(14)	57
Change in allowance for inventory reserves	1,298	640	(146)
Net gains on disposal of personal property	(54,071)	(27,057)	(26,982)
Net gains on disposal of real estate	3,281	(758)	(44)
Net gains on sales of investments	0	0	0
Net losses on equity investments	0	0	0
Deferred income taxes	72,407	323,980	112,434
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(60,806)	30,771	(26,160)
Inventories and parts	(5,775)	1,776	(13,492)
Prepaid expenses	94,359	(391,120)	(8,620)
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	29,879	(3,099)	159,126
Related party assets	(12,790)	(5,106)	3,857
Accounts payable and accrued expenses	96,309	(4,428)	6,454
Policy benefits and losses, claims and loss expenses payable	14,919	3,092	(159,793)
Other policyholders' funds and liabilities	0	0	0
Deferred income	10,959	(1,818)	966
Related party liabilities	1,136	(1,170)	(2,711)
Net cash provided by operating activities	1,428,893	980,494	958,940
Cash flow from investing activities:
Escrow deposits	(5,221)	6,617	4,299
Purchase of:
Property, plant and equipment	(1,441,475)	(2,309,406)	(1,869,968)
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity securities	0	0	0
Preferred stock	0
Real estate	0	0	(236)
Mortgage loans	0	0	0
Proceeds from sale and paydowns of:
Property, plant and equipment	537,484	687,375	606,271
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity securities	0	0	0
Preferred stock	0	0	0
Real estate	255	311
Mortgage loans	0	0	0
Net cash used by investing activities	(908,957)	(1,615,103)	(1,259,634)
Cash flow from financing activities:
Borrowings from credit facilities	912,408	1,118,912	897,311
Principal repayments on credit facilities	(652,728)	(347,486)	(299,748)
Debt issuance costs	(5,793)	(5,332)	(7,243)
Capital lease payments	(221,247)	(307,782)	(303,431)
Employee stock ownership plan shares		(206)	(418)
Common stock dividends paid	(49,019)	(29,404)	(39,179)
Net contribution from (to) related party	41,199	21,600
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	24,820	450,302	247,292
Effects of exchange rate on cash	6,441	(533)	(4,716)
Increase (decrease) in cash and cash equivalents	551,197	(184,840)	(58,118)
Cash and cash equivalents at the beginning of period	459,078	643,918	702,036
Cash and cash equivalents at the end of the period	1,010,275	459,078	643,918
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	25,720	33,928	21,708
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, net	1,578	1,469	1,361
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	(217)	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	(158)	(355)	(2,971)
Net losses on equity investments	(394)	(3,783)	5,739
Deferred income taxes	459	(2,847)	830
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	27,302	8,127	(2,438)
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	537	2,098	(1,449)
Related party assets	303	(539)	339
Accounts payable and accrued expenses	(3,497)	2,688	257
Policy benefits and losses, claims and loss expenses payable	(31,398)	(19,618)	(4,400)
Other policyholders' funds and liabilities	(2,053)	491	(117)
Deferred income	0	0	0
Related party liabilities	1,187	819	944
Net cash provided by operating activities	19,369	22,478	19,803
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	(69,929)	(60,590)	(53,878)
Fixed maturities investments	(18,823)	(13,001)	(33,775)
Equity securities	0	0	0
Preferred stock	0
Real estate	0	(328)	(187)
Mortgage loans	(18,035)	(18,050)	(20,031)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	69,669	59,056	58,767
Fixed maturities investments	20,854	25,386	12,305
Equity securities	0	185	8,608
Preferred stock	2,700	1,375	1,625
Real estate	0	0
Mortgage loans	17,659	4,126	5,881
Net cash used by investing activities	4,095	(1,841)	(20,685)
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
Employee stock ownership plan shares		0	0
Common stock dividends paid	0	0	0
Net contribution from (to) related party	(22,600)	(21,600)
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	(22,600)	(21,600)	0
Effects of exchange rate on cash	0	0	0
Increase (decrease) in cash and cash equivalents	864	(963)	(882)
Cash and cash equivalents at the beginning of period	4,794	5,757	6,639
Cash and cash equivalents at the end of the period	5,658	4,794	5,757
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	18,721	21,861	20,103
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	28,293	31,219	28,556
Amortization of premiums and accretion of discounts related to investments, net	12,651	11,848	11,746
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	55,321	51,857	35,387
Change in allowance for losses on trade receivables	(1)	0	(5)
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	(9,900)	(13,241)	308
Net losses on equity investments	0	0	0
Deferred income taxes	(4,455)	(3,240)	(6,453)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(6,012)	(769)	(2,767)
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	(36,162)	(24,447)	(25,957)
Other assets	(551)	(294)	(525)
Related party assets	0	0	(2)
Accounts payable and accrued expenses	113	(2,790)	3,552
Policy benefits and losses, claims and loss expenses payable	14,487	3,908	(71,927)
Other policyholders' funds and liabilities	4,283	(5,348)	5,124
Deferred income	608	0	0
Related party liabilities	9,737	1,977	(300)
Net cash provided by operating activities	87,133	72,541	(3,160)
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	0	(636)	(170)
Fixed maturities investments	(587,410)	(366,348)	(506,270)
Equity securities	(962)	(83)	(957)
Preferred stock	(16,144)
Real estate	(622)	(3,958)	(212)
Mortgage loans	(140,036)	(43,966)	(43,580)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	49	0	7,270
Fixed maturities investments	508,385	243,250	111,246
Equity securities	207	0	0
Preferred stock	0	1,000	0
Real estate	0	0
Mortgage loans	11,866	21,036	141,856
Net cash used by investing activities	(224,667)	(149,705)	(290,817)
Cash flow from financing activities:
Borrowings from credit facilities	9,600	2,500	0
Principal repayments on credit facilities	(9,860)	(2,500)	0
Debt issuance costs	0	0	0
Capital lease payments	0	0	0
Employee stock ownership plan shares		0	0
Common stock dividends paid	0	0	0
Net contribution from (to) related party	(18,599)	0
Investment contract deposits	517,856	234,640	400,123
Investment contract withdrawals	(213,864)	(151,022)	(132,833)
Net cash provided by financing activities	285,133	83,618	267,290
Effects of exchange rate on cash	0	0	0
Increase (decrease) in cash and cash equivalents	147,599	6,454	(26,687)
Cash and cash equivalents at the beginning of period	30,480	24,026	50,713
Cash and cash equivalents at the end of the period	178,079	30,480	24,026
Eliminations [Member]
Cash flow from operating activities:
Net earnings	(44,441)	(55,789)	(41,811)
Earnings from consolidated subsidiaries	44,441	55,789	41,811
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, net	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 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	12,000	0	0
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	(12,000)	0	0
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	0	0	0
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity securities	0	0	0
Preferred stock	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	0
Real estate	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
Employee stock ownership plan shares		0	0
Common stock dividends paid	0	0	0
Net contribution from (to) related party	0	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) in cash and cash equivalents	0	0	0
Cash and cash equivalents at the beginning of period	0	0	0
Cash and cash equivalents at the end of the period	$ 0	$ 0	$ 0