Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cash flow from operating activities:
Net earnings	$ 409,898	$ 266,365	$ 755,073	$ 354,091
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			343,863	332,240
Amortization of deferred policy acquisition costs	6,750	5,552	15,573	12,440
Amortization of premiums and accretion of discounts related to investments, net			9,151	6,926
Amortization of debt issuance costs			2,791	2,755
Interest credited to policyholders			31,894	24,241
Change in allowance for losses on trade receivables			222	(140)
Change in allowance for inventory reserves			8,352	106
Net gain on sale of real and personal property			(86,398)	(29,131)
Net losses on disposal of real estate	523	3,425	(3,907)	3,169
Net (gain) loss on sale of investments			(3,432)	(1,288)
Net losses on equity investments			(4,342)	2,254
Deferred income tax			138,916	80,198
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(3,771)	(28,288)
Inventories			(45,718)	386
Prepaid expenses			266,780	116,064
Capitalization of deferred policy acquisition costs			(17,807)	(13,404)
Other assets			(1,327)	(553)
Related party assets			(2,724)	2,785
Accounts payable and accrued expenses			91,548	112,489
Policy benefits and losses, claims and loss expenses payable			18,968	16,575
Other policyholders' funds and liabilities			(1,477)	(4,764)
Deferred income			7,592	13,237
Related party liabilities			(700)	(46)
Net cash provided by operating activities			1,519,120	1,002,342
Cash flow from investing activities:
Escrow deposits			(2,341)	1,266
Purchase of:
Property, plant and equipment			(1,039,688)	(662,259)
Short term investments			(21,669)	(19,222)
Fixed maturity investments			(415,640)	(160,755)
Equity securities			(36)	(719)
Preferred stock			(8,000)	(13,111)
Real estate			(124)	(223)
Mortgage loans			(106,963)	(72,316)
Proceeds from sale of:
Property, plant and equipment			306,946	314,335
Short term investments			16,673	23,180
Fixed maturity investments			230,043	226,656
Preferred stock			1,894	72
Mortgage loans			26,612	3,219
Net cash used by investing activities			(1,012,293)	(359,877)
Cash flow from financing activities:
Borrowings from credit facilities			987,048	585,723
Principal repayments on credit facilities			(227,072)	(386,779)
Payment of debt issuance costs			(2,092)	(3,477)
Capital lease payments			(87,500)	(122,720)
Common stock dividends paid			(19,608)	(9,804)
Net contribution from (to) related party				0
Investment contract deposits			199,426	114,288
Investment contract withdrawals			(116,021)	(102,466)
Net cash provided by (used in) financing activities			734,181	74,765
Effects on exchange rate on cash			(4,787)	3,986
Increase (decrease) in cash and cash equivalents			1,236,221	721,216
Cash and cash equivalents at the beginning of period			1,194,012	494,352
Cash and cash equivalents at the end of the period	2,430,233	1,215,568	2,430,233	1,215,568
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	409,898	266,365	755,073	354,091
Earnings from consolidated entities			(27,408)	(16,733)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			343,863	332,240
Amortization of deferred policy acquisition costs	0	0	0	0
Amortization of premiums and accretion of discounts related to investments, net			0	0
Amortization of debt issuance costs			2,791	2,755
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			253	(139)
Change in allowance for inventory reserves			8,352	106
Net gain on sale of real and personal property			(86,398)	(29,131)
Net losses on disposal of real estate	523	3,425	(3,907)	3,169
Net (gain) loss on sale of investments			0	0
Net losses on equity investments			0	0
Deferred income tax			140,780	79,947
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			6,159	(19,696)
Inventories			(45,718)	386
Prepaid expenses			266,780	116,064
Capitalization of deferred policy acquisition costs			0	0
Other assets			(1,033)	(181)
Related party assets			(1,161)	1,918
Accounts payable and accrued expenses			89,479	114,195
Policy benefits and losses, claims and loss expenses payable			15,250	14,300
Other policyholders' funds and liabilities			0	0
Deferred income			8,626	10,245
Related party liabilities			543	1,652
Net cash provided by operating activities			1,472,324	965,188
Cash flow from investing activities:
Escrow deposits			(2,341)	1,266
Purchase of:
Property, plant and equipment			(1,039,688)	(662,259)
Short term investments			0	0
Fixed maturity investments			0	0
Equity securities			0	0
Preferred stock			0	0
Real estate			(12)	0
Mortgage loans			(12)	0
Proceeds from sale of:
Property, plant and equipment			306,946	314,335
Short term investments			0	0
Fixed maturity investments			0	0
Preferred stock			0	0
Mortgage loans			0	0
Net cash used by investing activities			(735,107)	(346,658)
Cash flow from financing activities:
Borrowings from credit facilities			987,048	576,123
Principal repayments on credit facilities			(226,791)	(377,062)
Payment of debt issuance costs			(2,092)	(3,477)
Capital lease payments			(87,500)	(122,720)
Common stock dividends paid			(19,608)	(9,804)
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			651,057	81,659
Effects on exchange rate on cash			(4,787)	3,986
Increase (decrease) in cash and cash equivalents			1,383,487	704,175
Cash and cash equivalents at the beginning of period			1,010,275	459,078
Cash and cash equivalents at the end of the period	2,393,762	1,163,253	2,393,762	1,163,253
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	12,013	9,515	19,315	10,131
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	0	0
Amortization of premiums and accretion of discounts related to investments, net			754	786
Amortization of debt issuance costs			0	0
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			(30)	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	0	0
Net (gain) loss on sale of investments			(207)	(28)
Net losses on equity investments			(4,342)	2,254
Deferred income tax			865	804
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(148)	1,848
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			(179)	10
Related party assets			(1,563)	867
Accounts payable and accrued expenses			1,547	(2,618)
Policy benefits and losses, claims and loss expenses payable			174	(5,748)
Other policyholders' funds and liabilities			(222)	(5,093)
Deferred income			0	0
Related party liabilities			(2,098)	(135)
Net cash provided by operating activities			13,866	3,078
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(21,669)	(19,204)
Fixed maturity investments			(7,749)	(3,505)
Equity securities			0	0
Preferred stock			0	0
Real estate			0	0
Mortgage loans			(10,700)	(14,145)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			16,594	23,180
Fixed maturity investments			10,728	8,730
Preferred stock			0	0
Mortgage loans			565	555
Net cash used by investing activities			(12,231)	(4,389)
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	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 on exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			1,635	(1,311)
Cash and cash equivalents at the beginning of period			5,658	4,794
Cash and cash equivalents at the end of the period	7,293	3,483	7,293	3,483
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	6,276	4,823	8,093	6,602
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	6,750	5,552	15,573	12,440
Amortization of premiums and accretion of discounts related to investments, net			8,397	6,140
Amortization of debt issuance costs			0	0
Interest credited to policyholders			31,894	24,241
Change in allowance for losses on trade receivables			(1)	(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	0	0
Net (gain) loss on sale of investments			(3,225)	(1,260)
Net losses on equity investments			0	0
Deferred income tax			(2,729)	(553)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(9,782)	(10,440)
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(17,807)	(13,404)
Other assets			(115)	(382)
Related party assets			0	0
Accounts payable and accrued expenses			522	912
Policy benefits and losses, claims and loss expenses payable			3,544	8,023
Other policyholders' funds and liabilities			(1,255)	329
Deferred income			(1,034)	2,992
Related party liabilities			855	(1,563)
Net cash provided by operating activities			32,930	34,076
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			0	(18)
Fixed maturity investments			(407,891)	(157,250)
Equity securities			(36)	(719)
Preferred stock			(8,000)	(13,111)
Real estate			(112)	(223)
Mortgage loans			(96,251)	(58,171)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			79	0
Fixed maturity investments			219,315	217,926
Preferred stock			1,894	72
Mortgage loans			26,047	2,664
Net cash used by investing activities			(264,955)	(8,830)
Cash flow from financing activities:
Borrowings from credit facilities			0	9,600
Principal repayments on credit facilities			(281)	(9,717)
Payment of debt issuance costs			0	0
Capital lease payments			0	0
Common stock dividends paid			0	0
Net contribution from (to) related party				(18,599)
Investment contract deposits			199,426	114,288
Investment contract withdrawals			(116,021)	(102,466)
Net cash provided by (used in) financing activities			83,124	(6,894)
Effects on exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			(148,901)	18,352
Cash and cash equivalents at the beginning of period			178,079	30,480
Cash and cash equivalents at the end of the period	29,178	48,832	29,178	48,832
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(18,289)	(14,338)	(27,408)	(16,733)
Earnings from consolidated entities			27,408	16,733
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			0	0
Amortization of deferred policy acquisition costs	0	0	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	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
Equity securities			0	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	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	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 on 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	$ 0	$ 0