Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash flow from operating activities:
Net earnings	$ 266,365	$ 156,326	$ 354,091	$ 288,748
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			332,240	326,830
Amortization of deferred policy acquisition costs	5,552	6,515	12,440	12,579
Amortization of premiums and accretion of discounts related to investments, net			6,926	6,481
Amortization of debt issuance costs			2,755	2,100
Interest credited to policyholders			24,241	26,584
Change in allowance for losses on trade receivables			(140)	(113)
Change in allowance for inventory reserves			106	537
Net gain on sale of real and personal property			(29,131)	(34,677)
Net losses on disposal of real estate	3,425	(217)	3,169	(1,839)
Net (gain) loss on sale of investments			(1,288)	(7,595)
Net losses on equity investments			2,254	(2,553)
Deferred income tax			80,198	83,708
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(28,288)	2,471
Inventories			386	613
Prepaid expenses			116,064	(21,908)
Capitalization of deferred policy acquisition costs			(13,404)	(10,370)
Other assets			(553)	525
Related party assets			2,785	(5,019)
Accounts payable and accrued expenses			112,489	60,587
Policy benefits and losses, claims and loss expenses payable			16,575	10,709
Other policyholders' funds and liabilities			(4,764)	(4,136)
Deferred income			13,237	2,077
Related party liabilities			(46)	1,425
Net cash provided by operating activities			1,002,342	737,764
Cash flow from investing activities:
Escrow deposits			1,266	5,573
Purchase of:
Property, plant and equipment			(662,259)	(1,589,371)
Short term investments			(19,222)	(20,380)
Fixed maturity investments			(160,755)	(178,626)
Equity securities			(719)	(83)
Preferred stock			(13,111)	0
Real estate			(223)	(368)
Mortgage loans			(72,316)	(19,660)
Proceeds from sale of:
Property, plant and equipment			314,335	401,451
Short term investments			23,180	17,282
Fixed maturity investments			226,656	127,683
Preferred stock			72	0
Real estate			0	311
Mortgage loans			3,219	4,299
Net cash used by investing activities			(359,877)	(1,251,889)
Cash flow from financing activities:
Borrowings from credit facilities			585,723	658,745
Principal repayments on credit facilities			(386,779)	(143,634)
Payment of debt issuance costs			(3,477)	(2,301)
Capital lease payments			(122,720)	(180,902)
Employee stock ownership plan shares			0	(206)
Common stock dividends paid			(9,804)	(19,600)
Net contribution from (to) related party			0	21,600
Investment contract deposits			114,288	105,846
Investment contract withdrawals			(102,466)	(78,177)
Net cash provided by (used in) financing activities			74,765	361,371
Effects of exchange rate on cash			3,986	4,284
Increase (decrease) in cash and cash equivalents			721,216	(148,470)
Cash and cash equivalents at the beginning of period			494,352	673,701
Cash and cash equivalents at the end of the period	1,215,568	525,231	1,215,568	525,231
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	266,365	156,326	354,091	288,748
Earnings from consolidated entities			(16,733)	(22,745)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			332,240	326,830
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			2,755	2,100
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			(139)	(113)
Change in allowance for inventory reserves			106	537
Net gain on sale of real and personal property			(29,131)	(34,677)
Net losses on disposal of real estate	3,425	(217)	3,169	(1,839)
Net (gain) loss on sale of investments			0	0
Net losses on equity investments			0	0
Deferred income tax			79,947	87,544
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(19,696)	(987)
Inventories			386	613
Prepaid expenses			116,064	(21,908)
Capitalization of deferred policy acquisition costs			0	0
Other assets			(181)	(1,205)
Related party assets			1,918	(2,628)
Accounts payable and accrued expenses			114,195	59,091
Policy benefits and losses, claims and loss expenses payable			14,300	17,272
Other policyholders' funds and liabilities			0	0
Deferred income			10,245	2,077
Related party liabilities			1,652	406
Net cash provided by operating activities			965,188	699,116
Cash flow from investing activities:
Escrow deposits			1,266	5,573
Purchase of:
Property, plant and equipment			(662,259)	(1,589,371)
Short term investments			0	0
Fixed maturity investments			0	0
Equity securities			0	0
Preferred stock			0
Real estate			0	0
Mortgage loans			0	0
Proceeds from sale of:
Property, plant and equipment			314,335	401,451
Short term investments			0	0
Fixed maturity investments			0	0
Preferred stock			0
Real estate			0	311
Mortgage loans			0	0
Net cash used by investing activities			(346,658)	(1,182,036)
Cash flow from financing activities:
Borrowings from credit facilities			576,123	656,245
Principal repayments on credit facilities			(377,062)	(141,134)
Payment of debt issuance costs			(3,477)	(2,301)
Capital lease payments			(122,720)	(180,902)
Employee stock ownership plan shares				(206)
Common stock dividends paid			(9,804)	(19,600)
Net contribution from (to) related party			18,599	21,600
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			81,659	333,702
Effects of exchange rate on cash			3,986	4,284
Increase (decrease) in cash and cash equivalents			704,175	(144,934)
Cash and cash equivalents at the beginning of period			459,078	643,918
Cash and cash equivalents at the end of the period	1,163,253	498,984	1,163,253	498,984
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	9,515	7,228	10,131	13,916
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			786	754
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			(28)	(127)
Net losses on equity investments			2,254	(2,553)
Deferred income tax			804	(1,438)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			1,848	5,430
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			10	1,736
Related party assets			867	(2,391)
Accounts payable and accrued expenses			(2,618)	11
Policy benefits and losses, claims and loss expenses payable			(5,748)	(6,214)
Other policyholders' funds and liabilities			(5,093)	381
Deferred income			0	0
Related party liabilities			(135)	412
Net cash provided by operating activities			3,078	9,917
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(19,204)	(20,275)
Fixed maturity investments			(3,505)	(6,531)
Equity securities			0	0
Preferred stock			0
Real estate			0	(328)
Mortgage loans			(14,145)	(6,250)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			23,180	17,282
Fixed maturity investments			8,730	10,308
Preferred stock			0
Real estate			0	0
Mortgage loans			555	1,696
Net cash used by investing activities			(4,389)	(4,098)
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
Common stock dividends paid			0	0
Net contribution from (to) related party			0	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			(1,311)	5,819
Cash and cash equivalents at the beginning of period			4,794	5,757
Cash and cash equivalents at the end of the period	3,483	11,576	3,483	11,576
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	4,823	5,686	6,602	8,829
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	5,552	6,515	12,440	12,579
Amortization of premiums and accretion of discounts related to investments, net			6,140	5,727
Amortization of debt issuance costs			0	0
Interest credited to policyholders			24,241	26,584
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	0	0
Net (gain) loss on sale of investments			(1,260)	(7,468)
Net losses on equity investments			0	0
Deferred income tax			(553)	(2,398)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(10,440)	(1,972)
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(13,404)	(10,370)
Other assets			(382)	(6)
Related party assets			0	0
Accounts payable and accrued expenses			912	1,485
Policy benefits and losses, claims and loss expenses payable			8,023	(349)
Other policyholders' funds and liabilities			329	(4,517)
Deferred income			2,992	0
Related party liabilities			(1,563)	607
Net cash provided by operating activities			34,076	28,731
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(18)	(105)
Fixed maturity investments			(157,250)	(172,095)
Equity securities			(719)	(83)
Preferred stock			(13,111)
Real estate			(223)	(40)
Mortgage loans			(58,171)	(13,410)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			0	0
Fixed maturity investments			217,926	117,375
Preferred stock			72
Real estate			0	0
Mortgage loans			2,664	2,603
Net cash used by investing activities			(8,830)	(65,755)
Cash flow from financing activities:
Borrowings from credit facilities			9,600	2,500
Principal repayments on credit facilities			(9,717)	(2,500)
Payment of debt issuance costs			0	0
Capital lease payments			0	0
Employee stock ownership plan shares				0
Common stock dividends paid			0	0
Net contribution from (to) related party			(18,599)	0
Investment contract deposits			114,288	105,846
Investment contract withdrawals			(102,466)	(78,177)
Net cash provided by (used in) financing activities			(6,894)	27,669
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			18,352	(9,355)
Cash and cash equivalents at the beginning of period			30,480	24,026
Cash and cash equivalents at the end of the period	48,832	14,671	48,832	14,671
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(14,338)	(12,914)	(16,733)	(22,745)
Earnings from consolidated entities			16,733	22,745
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
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
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
Common stock dividends paid			0	0
Net contribution from (to) related party			0	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	$ 0	$ 0