Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Cash flow from operating activities:
Net earnings	$ 442,048	$ 370,857	$ 790,583
Earnings from consolidated subsidiaries	0	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	664,120	581,025	555,069
Amortization of deferred policy acquisition costs	31,219	28,556	24,514
Amortization of premiums and accretion of discounts related to investments, net	13,317	13,107	12,790
Amortization of debt issuance costs	4,426	3,923	3,868
Interest credited to policyholders	51,857	35,387	32,302
Change in allowance for losses on trade receivables	(14)	52	(120)
Change in allowance for inventory reserves	640	(146)	5,065
Net gains on disposal of real estate	(758)	(44)	(195,414)
Net gains on sales of investments	(13,596)	(2,663)	(6,269)
Net losses on equity investments	(3,783)	5,739	0
Deferred income taxes	317,893	106,811	(193,434)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	38,129	(31,365)	(15,329)
Inventories and parts	1,776	(13,492)	(12,384)
Prepaid expenses	(391,120)	(8,620)	(40,765)
Capitalization of deferred policy acquisition costs	(24,447)	(25,957)	(27,350)
Other assets	(1,295)	157,152	(165,968)
Related party assets	(5,645)	4,194	53,408
Accounts payable and accrued expenses	(4,530)	10,263	(36,980)
Policy benefits and losses, claims and loss expenses payable	(12,618)	(236,120)	161,121
Other policyholders' funds and liabilities	(4,857)	5,007	(109)
Deferred income	(1,818)	966	5,524
Related party liabilities	1,626	(2,067)	(616)
Net cash provided by operating activities	1,075,513	975,583	937,684
Cash flow from investing activities:
Escrow deposits	6,617	4,299	31,362
Purchase of:
Property, plant and equipment	(2,309,406)	(1,869,968)	(1,363,745)
Short term investments	(61,226)	(54,048)	(63,556)
Fixed maturities investments	(379,349)	(540,045)	(390,900)
Equity securities	(83)	(957)	(662)
Preferred stock	0	0	(1,000)
Real estate	(4,286)	(635)	(1,939)
Mortgage loans	(62,016)	(63,611)	(83,507)
Proceeds from sale and paydowns of:
Property, plant and equipment	687,375	606,271	699,803
Short term investments	59,056	66,037	67,790
Fixed maturities investments	268,636	123,551	163,469
Equity securities	185	8,608	0
Preferred stock	2,375	1,625	4,208
Real estate	311	0	2,783
Mortgage loans	25,162	147,737	37,590
Net cash used by investing activities	(1,766,649)	(1,571,136)	(898,304)
Cash flow from financing activities:
Borrowings from credit facilities	1,121,412	897,311	498,464
Principal repayments on credit facilities	(349,986)	(299,748)	(356,451)
Debt issuance costs	(5,332)	(7,243)	(5,111)
Capital lease payments	(307,782)	(303,431)	(296,363)
Employee stock ownership plan			(11,640)
Securitization deposits	0	0	(2,180)
Common stock dividends paid	(29,404)	(39,179)	(29,380)
Net contribution from (to) related party	0
Investment contract deposits	234,640	400,123	401,814
Investment contract withdrawals	(151,022)	(132,833)	(182,549)
Net cash provided by financing activities	512,320	514,582	16,604
Effects of exchange rate on cash	(533)	(4,716)	5,598
Increase (decrease) in cash and cash equivalents	(179,349)	(85,687)	61,582
Cash and cash equivalents at the beginning of period	673,701	759,388	697,806
Cash and cash equivalents at the end of the period	494,352	673,701	759,388
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	442,048	370,857	790,583
Earnings from consolidated subsidiaries	(55,789)	(41,811)	(46,990)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	664,120	581,025	555,069
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	4,426	3,923	3,868
Interest credited to policyholders	0	0	0
Change in allowance for losses on trade receivables	(14)	57	(31)
Change in allowance for inventory reserves	640	(146)	5,065
Net gains on disposal of personal property	(27,057)	(26,982)	(11,822)
Net gains on disposal of real estate	(758)	(44)	(195,414)
Net gains on sales of investments	0	0	0
Net losses on equity investments	0	0
Deferred income taxes	323,980	112,434	(182,358)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	30,771	(26,160)	(23,444)
Inventories and parts	1,776	(13,492)	(12,384)
Prepaid expenses	(391,120)	(8,620)	(40,765)
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	(3,099)	159,126	(167,579)
Related party assets	(5,106)	3,857	48,855
Accounts payable and accrued expenses	(4,428)	6,454	(36,384)
Policy benefits and losses, claims and loss expenses payable	3,092	(159,793)	168,687
Other policyholders' funds and liabilities	0	0	0
Deferred income	(1,818)	966	5,524
Related party liabilities	(1,170)	(2,711)	(1,884)
Net cash provided by operating activities	980,494	958,940	858,596
Cash flow from investing activities:
Escrow deposits	6,617	4,299	31,362
Purchase of:
Property, plant and equipment	(2,309,406)	(1,869,968)	(1,363,745)
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	(236)	(1,365)
Mortgage loans	0	0	0
Proceeds from sale and paydowns of:
Property, plant and equipment	687,375	606,271	699,803
Short term investments	0	0	0
Fixed maturities investments	0	0	0
Equity securities	0	0
Preferred stock	0	0	0
Real estate	311	0	2,783
Mortgage loans	0	0	0
Net cash used by investing activities	(1,615,103)	(1,259,634)	(631,162)
Cash flow from financing activities:
Borrowings from credit facilities	1,118,912	897,311	498,464
Principal repayments on credit facilities	(347,486)	(299,748)	(356,451)
Debt issuance costs	(5,332)	(7,243)	(5,111)
Capital lease payments	(307,782)	(303,431)	(296,363)
Employee stock ownership plan	(206)	(418)	(11,640)
Securitization deposits	0		(2,180)
Common stock dividends paid	(29,404)	(39,179)	(29,380)
Net contribution from (to) related party	21,600
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	450,302	247,292	(202,661)
Effects of exchange rate on cash	(533)	(4,716)	5,598
Increase (decrease) in cash and cash equivalents	(184,840)	(58,118)	30,371
Cash and cash equivalents at the beginning of period	643,918	702,036	671,665
Cash and cash equivalents at the end of the period	459,078	643,918	702,036
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	33,928	21,708	22,889
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	1,469	1,361	1,356
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	(355)	(2,971)	(1,703)
Net losses on equity investments	(3,783)	5,739
Deferred income taxes	(2,847)	830	(6,596)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	8,127	(2,438)	8,075
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	0	0	0
Other assets	2,098	(1,449)	1,810
Related party assets	(539)	339	4,553
Accounts payable and accrued expenses	2,688	257	648
Policy benefits and losses, claims and loss expenses payable	(19,618)	(4,400)	(10,623)
Other policyholders' funds and liabilities	491	(117)	1,194
Deferred income	0	0	0
Related party liabilities	819	944	318
Net cash provided by operating activities	22,478	19,803	21,921
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	(60,590)	(53,878)	(63,556)
Fixed maturities investments	(13,001)	(33,775)	(51,273)
Equity securities	0	0	0
Preferred stock	0	0	(1,000)
Real estate	(328)	(187)	(440)
Mortgage loans	(18,050)	(20,031)	(14,409)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	59,056	58,767	61,133
Fixed maturities investments	25,386	12,305	21,670
Equity securities	185	8,608
Preferred stock	1,375	1,625	4,208
Real estate	0	0	0
Mortgage loans	4,126	5,881	15,660
Net cash used by investing activities	(1,841)	(20,685)	(28,007)
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	0	0	0
Securitization deposits	0		0
Common stock dividends paid	0	0	0
Net contribution from (to) related party	(21,600)
Investment contract deposits	0	0	0
Investment contract withdrawals	0	0	0
Net cash provided by financing activities	(21,600)	0	0
Effects of exchange rate on cash	0	0	0
Increase (decrease) in cash and cash equivalents	(963)	(882)	(6,086)
Cash and cash equivalents at the beginning of period	5,757	6,639	12,725
Cash and cash equivalents at the end of the period	4,794	5,757	6,639
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	21,861	20,103	24,101
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	31,219	28,556	24,514
Amortization of premiums and accretion of discounts related to investments, net	11,848	11,746	11,434
Amortization of debt issuance costs	0	0	0
Interest credited to policyholders	51,857	35,387	32,302
Change in allowance for losses on trade receivables	0	(5)	(89)
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	(13,241)	308	(4,566)
Net losses on equity investments	0	0
Deferred income taxes	(3,240)	(6,453)	(4,480)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(769)	(2,767)	40
Inventories and parts	0	0	0
Prepaid expenses	0	0	0
Capitalization of deferred policy acquisition costs	(24,447)	(25,957)	(27,350)
Other assets	(294)	(525)	(199)
Related party assets	0	(2)	0
Accounts payable and accrued expenses	(2,790)	3,552	(1,244)
Policy benefits and losses, claims and loss expenses payable	3,908	(71,927)	3,057
Other policyholders' funds and liabilities	(5,348)	5,124	(1,303)
Deferred income	0	0	0
Related party liabilities	1,977	(300)	950
Net cash provided by operating activities	72,541	(3,160)	57,167
Cash flow from investing activities:
Escrow deposits	0	0	0
Purchase of:
Property, plant and equipment	0	0	0
Short term investments	(636)	(170)	0
Fixed maturities investments	(366,348)	(506,270)	(339,627)
Equity securities	(83)	(957)	(662)
Preferred stock	0	0	0
Real estate	(3,958)	(212)	(134)
Mortgage loans	(43,966)	(43,580)	(69,098)
Proceeds from sale and paydowns of:
Property, plant and equipment	0	0	0
Short term investments	0	7,270	6,657
Fixed maturities investments	243,250	111,246	141,799
Equity securities	0	0
Preferred stock	1,000	0	0
Real estate	0	0	0
Mortgage loans	21,036	141,856	21,930
Net cash used by investing activities	(149,705)	(290,817)	(239,135)
Cash flow from financing activities:
Borrowings from credit facilities	2,500	0	0
Principal repayments on credit facilities	(2,500)	0	0
Debt issuance costs	0	0	0
Capital lease payments	0	0	0
Employee stock ownership plan	0	0	0
Securitization deposits	0		0
Common stock dividends paid	0	0	0
Net contribution from (to) related party	0
Investment contract deposits	234,640	400,123	401,814
Investment contract withdrawals	(151,022)	(132,833)	(182,549)
Net cash provided by financing activities	83,618	267,290	219,265
Effects of exchange rate on cash	0	0	0
Increase (decrease) in cash and cash equivalents	6,454	(26,687)	37,297
Cash and cash equivalents at the beginning of period	24,026	50,713	13,416
Cash and cash equivalents at the end of the period	30,480	24,026	50,713
Eliminations [Member]
Cash flow from operating activities:
Net earnings	(55,789)	(41,811)	(46,990)
Earnings from consolidated subsidiaries	55,789	41,811	46,990
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
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	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	0	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	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
Preferred stock	0	0	0
Real estate	0	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	0	0	0
Securitization deposits	0		0
Common stock dividends paid	0	0	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) 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