Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Cash flow from operating activities:
Net earnings	$ 273,508	$ 349,866	$ 530,346	$ 688,211
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			394,400	359,804
Amortization of deferred policy acquisition costs	6,826	6,972	14,871	14,644
Amortization of premiums and accretion of discounts related to investments, inc			8,441	10,249
Amortization of debt issuance costs			3,427	3,356
Interest credited to policyholders			36,329	24,690
Change in allowance for losses on trade receivables			578	(5,494)
Change in allowance for inventory reserves			3,461	7,125
Net gain on sale of real and personal property	(46,803)	(64,342)	(102,464)	(128,690)
Net losses on disposal of real estate	1,715	1,872	2,736	4,179
Net (gain) loss on sale of investments			(917)	7,207
Net losses on equity investments			(2,745)	7,963
Deferred income tax			107,751	103,828
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(23,402)	32,342
Inventories			(13,520)	(14,416)
Prepaid expenses			(21,824)	3
Capitalization of deferred policy acquisition costs			(7,773)	(14,900)
Other assets			(8,751)	2,432
Related party assets			7,403	(1,640)
Accounts payable and accrued expenses			23,248	64,297
Policy benefits and losses, claims and loss expenses payable			(18,553)	11,460
Other policyholders' funds and liabilities			(554)	1,314
Deferred income			4,115	9,458
Related party liabilities			828	742
Net cash provided by operating activities			937,431	1,188,164
Cash flow from investing activities:
Escrow deposits			573	9,688
Purchase of:
Property, plant and equipment			(1,664,387)	(1,335,528)
Short term investments			(44,903)	(36,173)
Fixed maturity investments			(106,777)	(202,265)
Equity securities			(309)	(4,356)
Real estate			(537)	(4,931)
Mortgage loans			(97,702)	(75,635)
Proceeds from sale of:
Property, plant and equipment			408,279	329,611
Short term investments			15,959	33,373
Fixed maturity investments			389,216	106,527
Equity securities			300	717
Preferred stock			913	717
Mortgage loans			13,049	74,165
Net cash used by investing activities			(1,086,326)	(1,104,807)
Cash flow from financing activities:
Borrowings from credit facilities			704,960	792,654
Principal repayments on credit facilities			(351,893)	(441,019)
Payment of debt issuance costs			(4,018)	(3,942)
Capital lease payments			(59,752)	(65,831)
Securitization deposits			151	49
Common stock dividends paid			(14,118)	(19,608)
Investment contract deposits			132,630	169,017
Investment contract withdrawals			(174,256)	(139,917)
Net cash provided by (used in) financing activities			233,704	291,403
Effects on exchange rate on cash			(202)	(13,782)
Increase (decrease) in cash and cash equivalents			84,607	360,978
Cash and cash equivalents at the beginning of period			2,060,524	2,704,137
Cash and cash equivalents at the end of period	2,145,131	3,065,115	2,145,131	3,065,115
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	273,508	349,866	530,346	688,211
Earnings from consolidated entities			(27,092)	(15,915)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			394,400	359,804
Amortization of deferred policy acquisition costs	0	0	0	0
Amortization of premiums and accretion of discounts related to investments, inc			0	0
Amortization of debt issuance costs			3,427	3,356
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			646	(5,404)
Change in allowance for inventory reserves			3,461	7,125
Net gain on sale of real and personal property			(102,464)	(128,690)
Net losses on disposal of real estate	1,715	1,872	2,736	4,179
Net (gain) loss on sale of investments			0	0
Net losses on equity investments			0	0
Deferred income tax			108,291	107,281
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(23,200)	30,678
Inventories			(13,520)	(14,416)
Prepaid expenses			(21,824)	3
Capitalization of deferred policy acquisition costs			0	0
Other assets			(7,339)	2,877
Related party assets			6,279	(2,479)
Accounts payable and accrued expenses			38,562	65,366
Policy benefits and losses, claims and loss expenses payable			(10,609)	19,640
Other policyholders' funds and liabilities			0	0
Deferred income			4,532	7,809
Related party liabilities			671	460
Net cash provided by operating activities			887,303	1,129,885
Cash flow from investing activities:
Escrow deposits			573	9,688
Purchase of:
Property, plant and equipment			(1,664,387)	(1,335,528)
Short term investments			0	0
Fixed maturity investments			(97,331)	0
Equity securities			0	0
Real estate			(16)	0
Mortgage loans			0	0
Proceeds from sale of:
Property, plant and equipment			408,279	329,611
Short term investments			0	0
Fixed maturity investments			224,999	0
Equity securities			0
Preferred stock			0	0
Mortgage loans			0	0
Net cash used by investing activities			(1,127,883)	(996,229)
Cash flow from financing activities:
Borrowings from credit facilities			704,960	792,654
Principal repayments on credit facilities			(351,893)	(441,019)
Payment of debt issuance costs			(4,018)	(3,942)
Capital lease payments			(59,752)	(65,831)
Securitization deposits			151	49
Common stock dividends paid			(14,118)	(19,608)
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			275,330	262,303
Effects on exchange rate on cash			(202)	(13,782)
Increase (decrease) in cash and cash equivalents			34,548	382,177
Cash and cash equivalents at the beginning of period			2,034,242	2,643,213
Cash and cash equivalents at the end of period	2,068,790	3,025,390	2,068,790	3,025,390
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	12,238	4,519	21,748	11,115
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, inc			794	857
Amortization of debt issuance costs			0	0
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			(68)	(90)
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			(9)	(58)
Net losses on equity investments			(2,745)	7,963
Deferred income tax			501	(1,119)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(1,865)	(1,088)
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			134	(169)
Related party assets			1,124	839
Accounts payable and accrued expenses			1,446	1,396
Policy benefits and losses, claims and loss expenses payable			(2,859)	(3,381)
Other policyholders' funds and liabilities			(576)	112
Deferred income			0	0
Related party liabilities			425	(183)
Net cash provided by operating activities			18,050	16,194
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			0	(35,975)
Fixed maturity investments			(2,216)	(18,573)
Equity securities			(308)	(2,705)
Real estate			0	(4,920)
Mortgage loans			(7,300)	(12,715)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			15,959	33,373
Fixed maturity investments			7,180	10,587
Equity securities			296
Preferred stock			913	711
Mortgage loans			422	14,419
Net cash used by investing activities			14,946	(15,798)
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
Securitization deposits			0	0
Common stock dividends paid			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) in cash and cash equivalents			32,996	396
Cash and cash equivalents at the beginning of period			11,276	10,800
Cash and cash equivalents at the end of period	44,272	11,196	44,272	11,196
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	4,624	(613)	5,344	4,800
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	6,826	6,972	14,871	14,644
Amortization of premiums and accretion of discounts related to investments, inc			7,647	9,392
Amortization of debt issuance costs			0	0
Interest credited to policyholders			36,329	24,690
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			(908)	7,265
Net losses on equity investments			0	0
Deferred income tax			(1,041)	(2,334)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			1,663	2,752
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(7,773)	(14,900)
Other assets			(1,546)	(276)
Related party assets			0	0
Accounts payable and accrued expenses			(16,760)	(2,465)
Policy benefits and losses, claims and loss expenses payable			(5,085)	(4,799)
Other policyholders' funds and liabilities			22	1,202
Deferred income			(417)	1,649
Related party liabilities			(268)	465
Net cash provided by operating activities			32,078	42,085
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(44,903)	(198)
Fixed maturity investments			(7,230)	(183,692)
Equity securities			(1)	(1,651)
Real estate			(521)	(11)
Mortgage loans			(90,402)	(62,920)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			0	0
Fixed maturity investments			157,037	95,940
Equity securities			4
Preferred stock			0	6
Mortgage loans			12,627	59,746
Net cash used by investing activities			26,611	(92,780)
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
Securitization deposits			0	0
Common stock dividends paid			0	0
Investment contract deposits			132,630	169,017
Investment contract withdrawals			(174,256)	(139,917)
Net cash provided by (used in) financing activities			(41,626)	29,100
Effects on exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			17,063	(21,595)
Cash and cash equivalents at the beginning of period			15,006	50,124
Cash and cash equivalents at the end of period	32,069	28,529	32,069	28,529
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(16,862)	(3,906)	(27,092)	(15,915)
Earnings from consolidated entities			27,092	15,915
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, 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	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
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
Equity securities			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
Securitization deposits			0	0
Common stock dividends paid			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) 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 period	$ 0	$ 0	$ 0	$ 0