Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flow from operating activities:
Net earnings	$ 256,838	$ 338,345
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	193,475	178,144
Amortization of deferred policy acquisition costs	8,045	7,672
Amortization of premiums and accretion of discounts related to investments, inc	4,394	4,929
Amortization of debt issuance costs	1,456	1,473
Interest credited to policyholders	17,538	15,157
Change in allowance for losses on trade receivables	592	(6,151)
Change in allowance for inventory reserves	(327)	4,646
Net gain on sale of real and personal property	(55,661)	(64,348)
Net losses on disposal of real estate	1,021	2,307
Net (gain) loss on sale of investments	(1,914)	268
Net (gain) losses equity investments	(2,429)	1,551
Deferred income tax	34,108	63,493
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(17,435)	15,894
Inventories	(13,068)	(10,347)
Prepaid expenses	9,870	4,935
Capitalization of deferred policy acquisition costs	(3,177)	(7,398)
Other assets	(9,957)	1,935
Related party assets	3,132	484
Accounts payable and accrued expenses	33,112	74,676
Policy benefits and losses, claims and loss expenses payable	(12,098)	6,043
Other policyholders' funds and liabilities	3,986	1,187
Deferred income	11,999	14,448
Related party liabilities	2,197	2,028
Net cash provided by operating activities	465,697	651,371
Cash flow from investing activities:
Escrow deposits	(361)	4,789
Purchase of:
Property, plant and equipment	(773,577)	(646,137)
Short term investments	(9,957)	(22,017)
Fixed maturity investments	(3,251)	(36,488)
Equity Securities	(242)	(1,366)
Real estate	(415)	0
Mortgage loans	(52,450)	(42,561)
Proceeds from sale of:
Property, plant and equipment	193,455	159,180
Short term investments	11,745	18,073
Fixed maturity investments	336,859	55,808
Preferred stock	236	362
Mortgage loans	8,377	32,345
Net cash used by investing activities	(288,668)	(478,012)
Cash flow from financing activities:
Borrowings from credit facilities	445,493	393,264
Principal repayments on credit facilities	(232,824)	(145,369)
Payment of debt issuance costs	(2,688)	(1,069)
Capital lease payments	(34,168)	(34,982)
Common stock dividends paid	0	(9,804)
Investment contract deposits	51,239	85,767
Investment contract withdrawals	(83,331)	(62,911)
Net cash provided by (used in) financing activities	136,741	224,896
Effects on exchange rate on cash	2,830	(4,121)
Increase (decrease) cash and cash equivalents	316,600	394,134
Cash and cash equivalents at beginning of period	2,060,524	2,704,137
Cash and cash equivalents at end of period	2,377,124	3,098,271
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	256,838	338,345
Earnings from consolidated entities	(10,230)	(12,009)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	193,475	178,144
Amortization of deferred policy acquisition costs	0	0
Amortization of premiums and accretion of discounts related to investments, inc	0	0
Amortization of debt issuance costs	1,456	1,473
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	631	(6,075)
Change in allowance for inventory reserves	(327)	4,646
Net gain on sale of real and personal property	(55,661)	(64,348)
Net losses on disposal of real estate	1,021	2,307
Net (gain) loss on sale of investments	0	0
Net (gain) losses equity investments	0	0
Deferred income tax	32,087	61,948
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(17,964)	18,458
Inventories	(13,068)	(10,347)
Prepaid expenses	9,870	4,935
Capitalization of deferred policy acquisition costs	0	0
Other assets	(8,769)	2,177
Related party assets	3,645	747
Accounts payable and accrued expenses	52,573	78,549
Policy benefits and losses, claims and loss expenses payable	(7,590)	8,875
Other policyholders' funds and liabilities	0	0
Deferred income	12,441	14,501
Related party liabilities	1,547	1,251
Net cash provided by operating activities	451,975	623,577
Cash flow from investing activities:
Escrow deposits	(361)	4,789
Purchase of:
Property, plant and equipment	(773,577)	(646,137)
Short term investments	0	0
Fixed maturity investments	0	0
Equity Securities	0	0
Real estate	(16)
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	193,455	159,180
Short term investments	0	0
Fixed maturity investments	224,999	0
Preferred stock	0
Mortgage loans	0	0
Net cash used by investing activities	(355,500)	(482,168)
Cash flow from financing activities:
Borrowings from credit facilities	445,493	393,264
Principal repayments on credit facilities	(232,824)	(145,369)
Payment of debt issuance costs	(2,688)	(1,069)
Capital lease payments	(34,168)	(34,982)
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	168,833	202,040
Effects on exchange rate on cash	2,830	(4,121)
Increase (decrease) cash and cash equivalents	268,138	339,328
Cash and cash equivalents at beginning of period	2,034,242	2,643,213
Cash and cash equivalents at end of period	2,302,380	2,982,541
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	9,510	6,596
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0
Amortization of deferred policy acquisition costs	0	0
Amortization of premiums and accretion of discounts related to investments, inc	383	421
Amortization of debt issuance costs	0	0
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(39)	(76)
Change in allowance for inventory reserves	0	0
Net gain on sale of real and personal property	0	0
Net losses on disposal of real estate	0	0
Net (gain) loss on sale of investments	(34)	(31)
Net (gain) losses equity investments	(2,429)	1,551
Deferred income tax	2,085	127
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(411)	(2,107)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	(231)	(40)
Related party assets	(513)	(263)
Accounts payable and accrued expenses	(1,166)	(549)
Policy benefits and losses, claims and loss expenses payable	(4,047)	(1,237)
Other policyholders' funds and liabilities	(267)	(159)
Deferred income	0	0
Related party liabilities	655	517
Net cash provided by operating activities	3,496	4,750
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(9,216)	(21,966)
Fixed maturity investments	(495)	(9,839)
Equity Securities	(242)	(1,366)
Real estate	0
Mortgage loans	(7,300)	(6,975)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	11,676	18,073
Fixed maturity investments	3,490	6,852
Preferred stock	236
Mortgage loans	204	8,374
Net cash used by investing activities	(734)	(6,485)
Cash flow from financing activities:
Borrowings from credit facilities	0	0
Principal repayments on credit facilities	0	0
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	0	0
Effects on exchange rate on cash	0	0
Increase (decrease) cash and cash equivalents	2,762	(1,735)
Cash and cash equivalents at beginning of period	11,276	10,800
Cash and cash equivalents at end of period	14,038	9,065
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	720	5,413
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0
Amortization of deferred policy acquisition costs	8,045	7,672
Amortization of premiums and accretion of discounts related to investments, inc	4,011	4,508
Amortization of debt issuance costs	0	0
Interest credited to policyholders	17,538	15,157
Change in allowance for losses on trade receivables	0	0
Change in allowance for inventory reserves	0	0
Net gain on sale of real and personal property	0	0
Net losses on disposal of real estate	0	0
Net (gain) loss on sale of investments	(1,880)	299
Net (gain) losses equity investments	0	0
Deferred income tax	(64)	1,418
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	940	(457)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	(3,177)	(7,398)
Other assets	(957)	(202)
Related party assets	0	0
Accounts payable and accrued expenses	(18,295)	(3,324)
Policy benefits and losses, claims and loss expenses payable	(461)	(1,595)
Other policyholders' funds and liabilities	4,253	1,346
Deferred income	(442)	(53)
Related party liabilities	(5)	260
Net cash provided by operating activities	10,226	23,044
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(741)	(51)
Fixed maturity investments	(2,756)	(26,649)
Equity Securities	0	0
Real estate	(399)
Mortgage loans	(45,150)	(35,586)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	69	0
Fixed maturity investments	108,370	48,956
Preferred stock	0
Mortgage loans	8,173	23,971
Net cash used by investing activities	67,566	10,641
Cash flow from financing activities:
Borrowings from credit facilities	0	0
Principal repayments on credit facilities	0	0
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Investment contract deposits	51,239	85,767
Investment contract withdrawals	(83,331)	(62,911)
Net cash provided by (used in) financing activities	(32,092)	22,856
Effects on exchange rate on cash	0	0
Increase (decrease) cash and cash equivalents	45,700	56,541
Cash and cash equivalents at beginning of period	15,006	50,124
Cash and cash equivalents at end of period	60,706	106,665
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(10,230)	(12,009)
Earnings from consolidated entities	10,230	12,009
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	0	0
Amortization of deferred policy acquisition costs	0	0
Amortization of premiums and accretion of discounts related to investments, inc	0	0
Amortization of debt issuance costs	0	0
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	0	0
Change in allowance for inventory reserves	0	0
Net gain on sale of real and personal property	0	0
Net losses on disposal of real estate	0	0
Net (gain) loss on sale of investments	0	0
Net (gain) losses equity investments	0	0
Deferred income tax	0	0
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	0	0
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	0	0
Related party assets	0	0
Accounts payable and accrued expenses	0	0
Policy benefits and losses, claims and loss expenses payable	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	0	0
Related party liabilities	0	0
Net cash provided by operating activities	0	0
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	0	0
Fixed maturity investments	0	0
Equity Securities	0	0
Real estate	0
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	0	0
Fixed maturity investments	0	0
Preferred stock	0
Mortgage loans	0	0
Net cash used by investing activities	0	0
Cash flow from financing activities:
Borrowings from credit facilities	0	0
Principal repayments on credit facilities	0	0
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	0	0
Effects on exchange rate on cash	0	0
Increase (decrease) cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	$ 0	$ 0