Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flow from operating activities:
Net earnings	$ 132,422	$ 127,849
Earnings from consolidated entities	0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	157,278	142,722
Amortization of deferred policy acquisition costs	6,064	6,031
Amortization of premiums and accretion of discounts related to investments, net	3,275	3,219
Amortization of debt issuance costs	1,053	984
Interest credited to policyholders	14,218	8,060
Change in allowance for losses on trade receivables	(162)	38
Change in allowance for inventory reserves	367	2,139
Net gain on sale of real and personal property	(16,678)	(16,295)
Net losses on disposal of real estate	(1,622)	0
Net (gain) loss on sale of investments	(4,267)	506
Net losses on equity investments	(2,215)	1,176
Deferred income tax	29,763	37,574
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(18,215)	(14,543)
Inventories	2,110	(7,170)
Prepaid expenses	(15,720)	(17,999)
Capitalization of deferred policy acquisition costs	(5,090)	(5,808)
Other assets	3,337	(761)
Related party assets	(1,364)	2,205
Accounts payable and accrued expenses	89,716	86,430
Policy benefits and losses, claims and loss expenses payable	2,318	5,291
Other policyholders' funds and liabilities	(5,281)	(184)
Deferred income	8,527	7,732
Related party liabilities	1,092	474
Net cash provided by operating activities	380,926	369,670
Cash flow from investing activities:
Escrow deposits	1,968	(4,559)
Purchase of:
Property, plant and equipment	(847,248)	(548,147)
Short term investments	(8,689)	(14,390)
Fixed maturity investments	(76,515)	(103,121)
Equity securities	0	(46)
Preferred stock	0	(81)
Real estate	(328)	(80)
Mortgage loans	(9,410)	(8,262)
Proceeds from sale of:
Property, plant and equipment	160,754	187,546
Short term investments	6,982	20,416
Fixed maturity investments	38,258	14,645
Preferred stock	0	500
Real estate	311
Mortgage loans	1,678	9,402
Net cash used by investing activities	(732,239)	(446,177)
Cash flow from financing activities:
Borrowings from credit facilities	333,700	103,641
Principal repayments on credit facilities	(61,104)	(73,770)
Payment of debt issuance costs	(5)	(1,420)
Capital lease payments	(94,446)	(84,374)
Employee stock ownership plan shares	(131)	(57)
Securitization deposits	0
Common stock dividends paid	(9,796)	(9,795)
Investment contract deposits	61,515	76,343
Investment contract withdrawals	(37,054)	(38,763)
Net cash provided by (used in) financing activities	192,679	(28,195)
Effects of exchange rate on cash	4,764	(4,275)
Increase (decrease) in cash and cash equivalents	(153,870)	(108,977)
Cash and cash equivalents at the beginning of period	673,701	759,388
Cash and cash equivalents at the end of the period	519,831	650,411
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	132,422	127,849
Earnings from consolidated entities	(9,831)	(3,656)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation	157,278	142,722
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	1,053	984
Interest credited to policyholders	0	0
Change in allowance for losses on trade receivables	(162)	40
Change in allowance for inventory reserves	367	2,139
Net gain on sale of real and personal property	(16,678)	(16,295)
Net losses on disposal of real estate	(1,622)	0
Net (gain) loss on sale of investments	0	0
Net losses on equity investments	0	0
Deferred income tax	35,980	38,011
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(23,033)	(14,763)
Inventories	2,110	(7,170)
Prepaid expenses	(15,720)	(17,999)
Capitalization of deferred policy acquisition costs	0	0
Other assets	1,805	(132)
Related party assets	(925)	4,713
Accounts payable and accrued expenses	86,094	84,004
Policy benefits and losses, claims and loss expenses payable	8,802	4,208
Other policyholders' funds and liabilities	0	0
Deferred income	8,527	7,732
Related party liabilities	1,345	(913)
Net cash provided by operating activities	367,812	351,474
Cash flow from investing activities:
Escrow deposits	1,968	(4,559)
Purchase of:
Property, plant and equipment	(847,248)	(548,147)
Short term investments	0	0
Fixed maturity investments	0	0
Equity securities		0
Preferred stock		0
Real estate	0	0
Mortgage loans	0	0
Proceeds from sale of:
Property, plant and equipment	160,754	187,546
Short term investments	0	0
Fixed maturity investments	0	0
Real estate	311	0
Mortgage loans	0	0
Net cash used by investing activities	(684,215)	(365,160)
Cash flow from financing activities:
Borrowings from credit facilities	331,200	103,641
Principal repayments on credit facilities	(58,604)	(73,770)
Payment of debt issuance costs	(5)	(1,420)
Capital lease payments	(94,446)	(84,374)
Employee stock ownership plan shares	(131)	(57)
Securitization deposits		(9,795)
Common stock dividends paid	(9,796)
Investment contract deposits	0	0
Investment contract withdrawals	0	0
Net cash provided by (used in) financing activities	168,218	(65,775)
Effects of exchange rate on cash	4,764	(4,275)
Increase (decrease) in cash and cash equivalents	(143,421)	(83,736)
Cash and cash equivalents at the beginning of period	643,918	702,036
Cash and cash equivalents at the end of the period	500,497	618,300
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	6,688	2,168
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	374	301
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	(33)	(38)
Net losses on equity investments	(2,215)	1,176
Deferred income tax	(2,564)	36
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	5,078	2,331
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	0	0
Other assets	1,546	(243)
Related party assets	(439)	(2,508)
Accounts payable and accrued expenses	2,368	835
Policy benefits and losses, claims and loss expenses payable	(6,987)	(1,466)
Other policyholders' funds and liabilities	(414)	(577)
Deferred income	0	0
Related party liabilities	(315)	2,003
Net cash provided by operating activities	3,087	4,018
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	(8,689)	(14,220)
Fixed maturity investments	(5,149)	(12,754)
Equity securities		0
Preferred stock		0
Real estate	(328)	(59)
Mortgage loans	0	(2,287)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	6,942	20,287
Fixed maturity investments	4,196	2,869
Real estate	0	500
Mortgage loans	245	198
Net cash used by investing activities	(2,783)	(5,466)
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
Employee stock ownership plan shares	0	0
Securitization deposits		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	304	(1,448)
Cash and cash equivalents at the beginning of period	5,757	6,639
Cash and cash equivalents at the end of the period	6,061	5,191
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	3,143	1,488
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	6,064	6,031
Amortization of premiums and accretion of discounts related to investments, net	2,901	2,918
Amortization of debt issuance costs	0	0
Interest credited to policyholders	14,218	8,060
Change in allowance for losses on trade receivables	0	(2)
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	(4,234)	544
Net losses on equity investments	0	0
Deferred income tax	(3,653)	(473)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables	(260)	(2,111)
Inventories	0	0
Prepaid expenses	0	0
Capitalization of deferred policy acquisition costs	(5,090)	(5,808)
Other assets	(14)	(386)
Related party assets	0	0
Accounts payable and accrued expenses	1,254	1,591
Policy benefits and losses, claims and loss expenses payable	503	2,549
Other policyholders' funds and liabilities	(4,867)	393
Deferred income	0	0
Related party liabilities	62	(616)
Net cash provided by operating activities	10,027	14,178
Cash flow from investing activities:
Escrow deposits	0	0
Purchase of:
Property, plant and equipment	0	0
Short term investments	0	(170)
Fixed maturity investments	(71,366)	(90,367)
Equity securities		(46)
Preferred stock		(81)
Real estate	0	(21)
Mortgage loans	(9,410)	(5,975)
Proceeds from sale of:
Property, plant and equipment	0	0
Short term investments	40	129
Fixed maturity investments	34,062	11,776
Real estate	0	0
Mortgage loans	1,433	9,204
Net cash used by investing activities	(45,241)	(75,551)
Cash flow from financing activities:
Borrowings from credit facilities	2,500	0
Principal repayments on credit facilities	(2,500)	0
Payment of debt issuance costs	0	0
Capital lease payments	0	0
Employee stock ownership plan shares	0	0
Securitization deposits		0
Common stock dividends paid	0
Investment contract deposits	61,515	76,343
Investment contract withdrawals	(37,054)	(38,763)
Net cash provided by (used in) financing activities	24,461	37,580
Effects of exchange rate on cash	0	0
Increase (decrease) in cash and cash equivalents	(10,753)	(23,793)
Cash and cash equivalents at the beginning of period	24,026	50,713
Cash and cash equivalents at the end of the period	13,273	26,920
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(9,831)	(3,656)
Earnings from consolidated entities	9,831	3,656
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
Equity securities		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
Real estate	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
Employee stock ownership plan shares	0	0
Securitization deposits		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