Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flow from operating activities:
Net earnings	$ 87,726	$ 132,422
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	166,740	157,278
Amortization of deferred policy acquisition costs	6,888	6,064
Amortization of premiums and accretion of discounts related to investments, net	3,550	3,275
Amortization of debt issuance costs	1,297	1,053
Interest credited to policyholders	7,667	14,218
Change in allowance for losses on trade receivables	60	(162)
Change in allowance for inventory reserves	(99)	367
Net gain on sale of real and personal property	(1,069)	(16,678)
Net losses on disposal of real estate	(256)	(1,622)
Net (gain) loss on sale of investments	2,014	(4,267)
Net losses on equity investments	3,989	(2,215)
Deferred income tax	27,534	29,763
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(23,594)	(18,215)
Inventories	350	2,110
Prepaid expenses	(22,831)	(15,720)
Capitalization of deferred policy acquisition costs	(7,308)	(5,090)
Other assets	74	3,337
Related party assets	7,329	(1,364)
Accounts payable and accrued expenses	58,273	89,716
Policy benefits and losses, claims and loss expenses payable	528	2,318
Other policyholders' funds and liabilities	(3,426)	(5,281)
Deferred income	14,898	8,527
Related party liabilities	(249)	1,092
Net cash provided by operating activities	330,085	380,926
Cash flow from investing activities:
Escrow deposits	1,401	1,968
Purchase of:
Property, plant and equipment	(249,740)	(847,248)
Short term investments	(9,625)	(8,689)
Fixed maturity investments	(94,193)	(76,515)
Real estate	(192)	(328)
Mortgage loans	(33,300)	(9,410)
Proceeds from sale of:
Property, plant and equipment	76,412	160,754
Short term investments	2,448	6,982
Fixed maturity investments	110,165	38,258
Real estate	0	311
Mortgage loans	1,432	1,678
Net cash used by investing activities	(195,192)	(732,239)
Cash flow from financing activities:
Borrowings from credit facilities	377,051	333,700
Principal repayments on credit facilities	(154,089)	(61,104)
Payment of debt issuance costs	(1,677)	(5)
Capital lease payments	(68,554)	(94,446)
Net contribution from (to) related party	18,599	0
Employee stock ownership plan shares	0	(131)
Common stock dividends paid	0	(9,796)
Investment contract deposits	75,366	61,515
Investment contract withdrawals	(51,633)	(37,054)
Net cash provided by (used in) financing activities	195,063	192,679
Effects of exchange rate on cash	766	4,764
Increase (decrease) in cash and cash equivalents	330,722	(153,870)
Cash and cash equivalents at the beginning of period	494,352	673,701
Cash and cash equivalents at the end of the period	825,074	519,831
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	87,726	132,422
Earnings from consolidated entities	(2,395)	(9,831)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	166,740	157,278
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	1,297	1,053
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	60	(162)
Change in allowance for inventory reserves	(99)	367
Net gain on sale of real and personal property	(1,069)	(16,678)
Net losses on disposal of real estate	(256)	(1,622)
Net (gain) loss on sale of investments	0	0
Net losses on equity investments	0	0
Deferred income tax	28,939	35,980
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(24,749)	(23,033)
Inventories	350	2,110
Prepaid expenses	(22,831)	(15,720)
Capitalization of deferred policy acquisition costs	0	0
Other assets	758	1,805
Related party assets	7,302	(925)
Accounts payable and accrued expenses	56,522	86,094
Policy benefits and losses, claims and loss expenses payable	294	8,802
Other policyholders' funds and liabilities	0	0
Deferred income	11,238	8,527
Related party liabilities	1,867	1,345
Net cash provided by operating activities	311,694	367,812
Cash flow from investing activities:
Escrow deposits	1,401	1,968
Purchase of:
Property, plant and equipment	(249,740)	(847,248)
Short term investments	0	0
Fixed maturity investments	0	0
Real estate	0	0
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	76,412	160,754
Short term investments	0	0
Fixed maturity investments	0	0
Real estate		311
Mortgage loans	0	0
Net cash used by investing activities	(171,927)	(684,215)
Cash flow from financing activities:
Borrowings from credit facilities	367,451	331,200
Principal repayments on credit facilities	(144,489)	(58,604)
Payment of debt issuance costs	(1,677)	(5)
Capital lease payments	(68,554)	(94,446)
Net contribution from (to) related party	18,599
Employee stock ownership plan shares		(131)
Common stock dividends paid		(9,796)
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	171,330	168,218
Effects of exchange rate on cash	766	4,764
Increase (decrease) in cash and cash equivalents	311,863	(143,421)
Cash and cash equivalents at the beginning of period	459,078	643,918
Cash and cash equivalents at the end of the period	770,941	500,497
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	616	6,688
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	395	374
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	(13)	(33)
Net losses on equity investments	3,989	(2,215)
Deferred income tax	1,070	(2,564)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	5,725	5,078
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	(340)	1,546
Related party assets	27	(439)
Accounts payable and accrued expenses	(246)	2,368
Policy benefits and losses, claims and loss expenses payable	(2,769)	(6,987)
Other policyholders' funds and liabilities	(4,089)	(414)
Deferred income	0	0
Related party liabilities	(834)	(315)
Net cash provided by operating activities	3,531	3,087
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(8,989)	(8,689)
Fixed maturity investments	(1,864)	(5,149)
Real estate	0	(328)
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	1,980	6,942
Fixed maturity investments	4,402	4,196
Real estate		0
Mortgage loans	265	245
Net cash used by investing activities	(4,206)	(2,783)
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
Employee stock ownership plan shares		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 of exchange rate on cash	0	0
Increase (decrease) in cash and cash equivalents	(675)	304
Cash and cash equivalents at the beginning of period	4,794	5,757
Cash and cash equivalents at the end of the period	4,119	6,061
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	1,779	3,143
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	6,888	6,064
Amortization of premiums and accretion of discounts related to investments, net	3,155	2,901
Amortization of debt issuance costs	0	0
Interest credited to policyholders	7,667	14,218
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	2,027	(4,234)
Net losses on equity investments	0	0
Deferred income tax	(2,475)	(3,653)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(4,570)	(260)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	(7,308)	(5,090)
Other assets	(344)	(14)
Related party assets	0	0
Accounts payable and accrued expenses	1,997	1,254
Policy benefits and losses, claims and loss expenses payable	3,003	503
Other policyholders' funds and liabilities	663	(4,867)
Deferred income	3,660	0
Related party liabilities	(1,282)	62
Net cash provided by operating activities	14,860	10,027
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(636)	0
Fixed maturity investments	(92,329)	(71,366)
Real estate	(192)	0
Mortgage loans	(33,300)	(9,410)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	468	40
Fixed maturity investments	105,763	34,062
Real estate		0
Mortgage loans	1,167	1,433
Net cash used by investing activities	(19,059)	(45,241)
Cash flow from financing activities:
Borrowings from credit facilities	9,600	2,500
Principal repayments on credit facilities	(9,600)	(2,500)
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Net contribution from (to) related party	0
Employee stock ownership plan shares		0
Common stock dividends paid		0
Investment contract deposits	75,366	61,515
Investment contract withdrawals	(51,633)	(37,054)
Net cash provided by (used in) financing activities	23,733	24,461
Effects of exchange rate on cash	0	0
Increase (decrease) in cash and cash equivalents	19,534	(10,753)
Cash and cash equivalents at the beginning of period	30,480	24,026
Cash and cash equivalents at the end of the period	50,014	13,273
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(2,395)	(9,831)
Earnings from consolidated entities	2,395	9,831
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
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
Real estate		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
Employee stock ownership plan shares		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 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