Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flow from operating activities:
Net earnings	$ 334,002	$ 345,175
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	178,144	172,040
Amortization of deferred policy acquisition costs	7,672	8,823
Amortization of premiums and accretion of discounts related to investments, inc	4,929	4,361
Amortization of debt issuance costs	1,473	1,332
Interest credited to policyholders	15,157	15,583
Change in allowance for losses on trade receivables	(6,151)	(484)
Change in allowance for inventory reserves	4,646	3,403
Net gain on sale of real and personal property	(64,348)	(50,323)
Net losses on disposal of real estate	2,307	(4,430)
Net (gain) loss on sale of investments	268	(2,469)
Net (gain) losses equity investments	1,551	(2,231)
Deferred income tax	63,493	82,374
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	15,894	(8,082)
Inventories	(10,347)	(15,765)
Prepaid expenses	4,935	162,706
Capitalization of deferred policy acquisition costs	(7,398)	(8,990)
Other assets	1,935	(853)
Related party assets	484	562
Accounts payable and accrued expenses	74,676	71,599
Policy benefits and losses, claims and loss expenses payable	10,386	9,064
Other policyholders' funds and liabilities	1,187	(1,430)
Deferred income	14,448	11,863
Related party liabilities	2,028	385
Net cash provided by operating activities	651,371	794,213
Cash flow from investing activities:
Escrow deposits	4,789	1,887
Purchase of:
Property, plant and equipment	(646,137)	(508,411)
Short term investments	(22,017)	(11,810)
Fixed maturity investments	(36,488)	(281,507)
Equity securities	(1,366)	0
Preferred stock	0	(8,000)
Real estate	0	(67)
Mortgage loans	(42,561)	(42,538)
Proceeds from sale of:
Property, plant and equipment	159,180	182,146
Short term investments	18,073	12,558
Fixed maturity investments	55,808	126,956
Preferred stock	362	0
Mortgage loans	32,345	5,628
Net cash used by investing activities	(478,012)	(523,158)
Cash flow from financing activities:
Borrowings from credit facilities	393,264	161,854
Principal repayments on credit facilities	(145,369)	(109,334)
Payment of debt issuance costs	(1,069)	(352)
Capital lease payments	(34,982)	(45,170)
Common stock dividends paid	(9,804)	0
Investment contract deposits	85,767	113,779
Investment contract withdrawals	(62,911)	(64,332)
Net cash provided by (used in) financing activities	224,896	56,445
Effects on exchange rate on cash	(4,121)	(1,531)
Increase (decrease) cash and cash equivalents	394,134	325,969
Cash and cash equivalents at the beginning of period	2,704,137	1,194,012
Cash and cash equivalents at the end of the period	3,098,271	1,519,981
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	334,002	345,175
Earnings from consolidated entities	(7,666)	(9,119)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	178,144	172,040
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	1,473	1,332
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(6,075)	(478)
Change in allowance for inventory reserves	4,646	3,403
Net gain on sale of real and personal property	(64,348)	(50,323)
Net losses on disposal of real estate	2,307	(4,430)
Net (gain) loss on sale of investments	0	0
Net (gain) losses equity investments	0	0
Deferred income tax	61,948	81,341
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	18,458	(1,658)
Inventories	(10,347)	(15,765)
Prepaid expenses	4,935	162,706
Capitalization of deferred policy acquisition costs	0	0
Other assets	2,177	(436)
Related party assets	747	302
Accounts payable and accrued expenses	78,549	60,902
Policy benefits and losses, claims and loss expenses payable	8,875	5,942
Other policyholders' funds and liabilities	0	0
Deferred income	14,501	12,125
Related party liabilities	1,251	1,422
Net cash provided by operating activities	623,577	764,481
Cash flow from investing activities:
Escrow deposits	4,789	1,887
Purchase of:
Property, plant and equipment	(646,137)	(508,411)
Short term investments	0	0
Fixed maturity investments	0	0
Equity securities	0
Preferred stock	0	0
Real estate	0	0
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	159,180	182,146
Short term investments	0	0
Fixed maturity investments	0	0
Preferred stock	0
Mortgage loans	0	0
Net cash used by investing activities	(482,168)	(324,378)
Cash flow from financing activities:
Borrowings from credit facilities	393,264	161,854
Principal repayments on credit facilities	(145,369)	(109,206)
Payment of debt issuance costs	(1,069)	(352)
Capital lease payments	(34,982)	(45,170)
Common stock dividends paid	(9,804)
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	202,040	7,126
Effects on exchange rate on cash	(4,121)	(1,531)
Increase (decrease) cash and cash equivalents	339,328	445,698
Cash and cash equivalents at the beginning of period	2,643,213	1,010,275
Cash and cash equivalents at the end of the period	2,982,541	1,455,973
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	6,596	7,302
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	421	413
Amortization of debt issuance costs	0	0
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(76)	(5)
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	(31)	(37)
Net (gain) losses equity investments	1,551	(2,231)
Deferred income tax	127	604
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(2,107)	(520)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	(40)	(323)
Related party assets	(263)	260
Accounts payable and accrued expenses	(549)	225
Policy benefits and losses, claims and loss expenses payable	(1,237)	352
Other policyholders' funds and liabilities	(159)	(461)
Deferred income	0	0
Related party liabilities	517	(1,972)
Net cash provided by operating activities	4,750	3,607
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(21,966)	(11,680)
Fixed maturity investments	(9,839)	(7,466)
Equity securities	(1,366)
Preferred stock	0	0
Real estate	0	0
Mortgage loans	(6,975)	(4,850)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	18,073	12,558
Fixed maturity investments	6,852	5,136
Preferred stock	362
Mortgage loans	8,374	283
Net cash used by investing activities	(6,485)	(6,019)
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
Common stock dividends paid	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	(1,735)	(2,412)
Cash and cash equivalents at the beginning of period	10,800	5,658
Cash and cash equivalents at the end of the period	9,065	3,246
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	1,070	1,817
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	7,672	8,823
Amortization of premiums and accretion of discounts related to investments, inc	4,508	3,948
Amortization of debt issuance costs	0	0
Interest credited to policyholders	15,157	15,583
Change in allowance for losses on trade receivables	0	(1)
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	299	(2,432)
Net (gain) losses equity investments	0	0
Deferred income tax	1,418	429
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(457)	(5,904)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	(7,398)	(8,990)
Other assets	(202)	(94)
Related party assets	0	0
Accounts payable and accrued expenses	(3,324)	10,472
Policy benefits and losses, claims and loss expenses payable	2,748	2,770
Other policyholders' funds and liabilities	1,346	(969)
Deferred income	(53)	(262)
Related party liabilities	260	935
Net cash provided by operating activities	23,044	26,125
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(51)	(130)
Fixed maturity investments	(26,649)	(274,041)
Equity securities	0
Preferred stock	0	(8,000)
Real estate	0	(67)
Mortgage loans	(35,586)	(37,688)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	0	0
Fixed maturity investments	48,956	121,820
Preferred stock	0
Mortgage loans	23,971	5,345
Net cash used by investing activities	10,641	(192,761)
Cash flow from financing activities:
Borrowings from credit facilities	0	0
Principal repayments on credit facilities	0	(128)
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Common stock dividends paid	0
Investment contract deposits	85,767	113,779
Investment contract withdrawals	(62,911)	(64,332)
Net cash provided by (used in) financing activities	22,856	49,319
Effects on exchange rate on cash	0	0
Increase (decrease) cash and cash equivalents	56,541	(117,317)
Cash and cash equivalents at the beginning of period	50,124	178,079
Cash and cash equivalents at the end of the period	106,665	60,762
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(7,666)	(9,119)
Earnings from consolidated entities	7,666	9,119
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
Preferred stock	0	0
Real estate	0	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
Common stock dividends paid	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 the beginning of period	0	0
Cash and cash equivalents at the end of the period	$ 0	$ 0