Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flow from operating activities:
Net earnings	$ 345,175	$ 87,726
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	172,040	166,740
Amortization of deferred policy acquisition costs	8,823	6,888
Amortization of premiums and accretion of discounts related to investments, net	4,361	3,550
Amortization of debt issuance costs	1,332	1,297
Interest credited to policyholders	15,583	7,667
Change in allowance for losses on trade receivables	(484)	60
Change in allowance for inventory reserves	3,403	(99)
Net gain on sale of real and personal property	(50,323)	(1,069)
Net losses on disposal of real estate	(4,430)	(256)
Net (gain) loss on sale of investments	(2,469)	2,014
Net losses on equity investments	(2,231)	3,989
Deferred income tax	82,374	27,534
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(8,082)	(23,594)
Inventories	(15,765)	350
Prepaid expenses	162,706	(22,831)
Capitalization of deferred policy acquisition costs	(8,990)	(7,308)
Other assets	(853)	74
Related party assets	562	7,329
Accounts payable and accrued expenses	71,599	58,273
Policy benefits and losses, claims and loss expenses payable	9,064	528
Other policyholders' funds and liabilities	(1,430)	(3,426)
Deferred income	11,863	14,898
Related party liabilities	385	(249)
Net cash provided by operating activities	794,213	330,085
Cash flow from investing activities:
Escrow deposits	1,887	1,401
Purchase of:
Property, plant and equipment	(508,411)	(249,740)
Short term investments	(11,810)	(9,625)
Fixed maturity investments	(281,507)	(94,193)
Preferred stock	(8,000)	0
Real estate	(67)	(192)
Mortgage loans	(42,538)	(33,300)
Proceeds from sale of:
Property, plant and equipment	182,146	76,412
Short term investments	12,558	2,448
Fixed maturity investments	126,956	110,165
Mortgage loans	5,628	1,432
Net cash used by investing activities	(523,158)	(195,192)
Cash flow from financing activities:
Borrowings from credit facilities	161,854	377,051
Principal repayments on credit facilities	(109,334)	(154,089)
Payment of debt issuance costs	(352)	(1,677)
Capital lease payments	(45,170)	(68,554)
Net contribution from (to) related party	0	18,599
Investment contract deposits	113,779	75,366
Investment contract withdrawals	(64,332)	(51,633)
Net cash provided by (used in) financing activities	56,445	195,063
Effects of exchange rate on cash	(1,531)	766
Increase (decrease) in cash and cash equivalents	325,969	330,722
Cash and cash equivalents at the beginning of period	1,194,012	494,352
Cash and cash equivalents at the end of the period	1,519,981	825,074
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	345,175	87,726
Earnings from consolidated entities	(9,119)	(2,395)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	172,040	166,740
Amortization of deferred policy acquisition costs	0	0
Amortization of premiums and accretion of discounts related to investments, net	0	0
Amortization of debt issuance costs	1,332	1,297
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(478)	60
Change in allowance for inventory reserves	3,403	(99)
Net gain on sale of real and personal property	(50,323)	(1,069)
Net losses on disposal of real estate	(4,430)	(256)
Net (gain) loss on sale of investments	0	0
Net losses on equity investments	0	0
Deferred income tax	81,341	28,939
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(1,658)	(24,749)
Inventories	(15,765)	350
Prepaid expenses	162,706	(22,831)
Capitalization of deferred policy acquisition costs	0	0
Other assets	(436)	758
Related party assets	302	7,302
Accounts payable and accrued expenses	60,902	56,522
Policy benefits and losses, claims and loss expenses payable	5,942	294
Other policyholders' funds and liabilities	0	0
Deferred income	12,125	11,238
Related party liabilities	1,422	1,867
Net cash provided by operating activities	764,481	311,694
Cash flow from investing activities:
Escrow deposits	1,887	1,401
Purchase of:
Property, plant and equipment	(508,411)	(249,740)
Short term investments	0	0
Fixed maturity investments	0	0
Preferred stock	0
Real estate	0	0
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	182,146	76,412
Short term investments	0	0
Fixed maturity investments	0	0
Mortgage loans	0	0
Net cash used by investing activities	(324,378)	(171,927)
Cash flow from financing activities:
Borrowings from credit facilities	161,854	367,451
Principal repayments on credit facilities	(109,206)	(144,489)
Payment of debt issuance costs	(352)	(1,677)
Capital lease payments	(45,170)	(68,554)
Net contribution from (to) related party		18,599
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	7,126	171,330
Effects of exchange rate on cash	(1,531)	766
Increase (decrease) in cash and cash equivalents	445,698	311,863
Cash and cash equivalents at the beginning of period	1,010,275	459,078
Cash and cash equivalents at the end of the period	1,455,973	770,941
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	7,302	616
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, net	413	395
Amortization of debt issuance costs	0	0
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(5)	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	(37)	(13)
Net losses on equity investments	(2,231)	3,989
Deferred income tax	604	1,070
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(520)	5,725
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	(323)	(340)
Related party assets	260	27
Accounts payable and accrued expenses	225	(246)
Policy benefits and losses, claims and loss expenses payable	352	(2,769)
Other policyholders' funds and liabilities	(461)	(4,089)
Deferred income	0	0
Related party liabilities	(1,972)	(834)
Net cash provided by operating activities	3,607	3,531
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(11,680)	(8,989)
Fixed maturity investments	(7,466)	(1,864)
Preferred stock	0
Real estate	0	0
Mortgage loans	(4,850)	0
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	12,558	1,980
Fixed maturity investments	5,136	4,402
Mortgage loans	283	265
Net cash used by investing activities	(6,019)	(4,206)
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
Net contribution from (to) related party		0
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	0	0
Effects of exchange rate on cash	0	0
Increase (decrease) in cash and cash equivalents	(2,412)	(675)
Cash and cash equivalents at the beginning of period	5,658	4,794
Cash and cash equivalents at the end of the period	3,246	4,119
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	1,817	1,779
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	8,823	6,888
Amortization of premiums and accretion of discounts related to investments, net	3,948	3,155
Amortization of debt issuance costs	0	0
Interest credited to policyholders	15,583	7,667
Change in allowance for losses on trade receivables	(1)	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	(2,432)	2,027
Net losses on equity investments	0	0
Deferred income tax	429	(2,475)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(5,904)	(4,570)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	(8,990)	(7,308)
Other assets	(94)	(344)
Related party assets	0	0
Accounts payable and accrued expenses	10,472	1,997
Policy benefits and losses, claims and loss expenses payable	2,770	3,003
Other policyholders' funds and liabilities	(969)	663
Deferred income	(262)	3,660
Related party liabilities	935	(1,282)
Net cash provided by operating activities	26,125	14,860
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(130)	(636)
Fixed maturity investments	(274,041)	(92,329)
Preferred stock	(8,000)
Real estate	(67)	(192)
Mortgage loans	(37,688)	(33,300)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	0	468
Fixed maturity investments	121,820	105,763
Mortgage loans	5,345	1,167
Net cash used by investing activities	(192,761)	(19,059)
Cash flow from financing activities:
Borrowings from credit facilities	0	9,600
Principal repayments on credit facilities	(128)	(9,600)
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Net contribution from (to) related party		0
Investment contract deposits	113,779	75,366
Investment contract withdrawals	(64,332)	(51,633)
Net cash provided by (used in) financing activities	49,319	23,733
Effects of exchange rate on cash	0	0
Increase (decrease) in cash and cash equivalents	(117,317)	19,534
Cash and cash equivalents at the beginning of period	178,079	30,480
Cash and cash equivalents at the end of the period	60,762	50,014
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(9,119)	(2,395)
Earnings from consolidated entities	9,119	2,395
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, net	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 losses on 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
Preferred stock	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
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
Net contribution from (to) related party		0
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	0	0
Effects of exchange rate on cash	0	0
Increase (decrease) in 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