Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Cash flow from operating activities:
Net earnings	$ 182,985	$ 30,932	$ 537,076	$ 319,680
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			495,794	494,753
Amortization of deferred policy acquisition costs	6,572	8,046	19,012	20,625
Amortization of premiums and accretion of discounts related to investments, net			10,197	9,848
Amortization of debt issuance costs			4,645	3,275
Interest credited to policyholders			38,672	38,169
Change in allowance for losses on trade receivables			(574)	(76)
Change in allowance for inventory reserves			3,259	(85)
Net gain on sale of real and personal property	(10,952)	(2,151)	(40,083)	(32,526)
Net losses on disposal of real estate	1,124	528	4,293	(1,311)
Net (gain) loss on sale of investments			(5,644)	(8,777)
Net losses on equity investments			669	(3,749)
Deferred income tax			117,025	87,805
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(39,499)	24,759
Inventories			(6,349)	589
Prepaid expenses			112,428	(16,402)
Capitalization of deferred policy acquisition costs			(24,903)	(17,530)
Other assets			30,120	(293)
Related party assets			(20,794)	(17,507)
Accounts payable and accrued expenses			97,151	51,754
Policy benefits and losses, claims and loss expenses payable			14,096	3,974
Other policyholders' funds and liabilities			24,677	(2,123)
Deferred income			6,851	(2,317)
Related party liabilities			(1,566)	446
Net cash provided by operating activities			1,376,553	952,981
Cash flow from investing activities:
Escrow deposits			(1,978)	7,153
Purchase of:
Property, plant and equipment			(961,995)	(1,917,862)
Short term investments			(38,790)	(47,457)
Fixed maturity investments			(352,307)	(267,909)
Equity securities			(838)	(83)
Preferred stock			(16,144)	0
Real estate			(274)	(484)
Mortgage loans			(92,281)	(43,085)
Proceeds from sale of:
Property, plant and equipment			434,860	599,797
Short term investments			38,830	46,859
Fixed maturity investments			331,407	193,196
Equity securities			72	185
Preferred stock			1,200	0
Real estate			0	311
Mortgage loans			4,744	9,052
Net cash used by investing activities			(653,494)	(1,420,327)
Cash flow from financing activities:
Borrowings from credit facilities			790,532	867,862
Principal repayments on credit facilities			(568,068)	(225,332)
Payment of debt issuance costs			(5,020)	(3,671)
Capital lease payments			(173,520)	(247,188)
Employee stock ownership plan shares			0	(206)
Securitization deposits				(19,600)
Common stock dividends paid			(49,019)	(19,600)
Net contribution from (to) related party			22,600	0
Investment contract deposits			326,055	171,465
Investment contract withdrawals			(169,008)	(122,948)
Net cash provided by (used in) financing activities			174,552	420,382
Effects of exchange rate on cash			6,877	5,214
Increase (decrease) in cash and cash equivalents			904,488	(41,750)
Cash and cash equivalents at the beginning of period			494,352	673,701
Cash and cash equivalents at the end of the period	1,398,840	631,951	1,398,840	631,951
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	182,985	30,932	537,076	319,680
Earnings from consolidated entities			(32,850)	(37,941)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			495,794	494,753
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			4,645	3,275
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			(573)	(76)
Change in allowance for inventory reserves			3,259	(85)
Net gain on sale of real and personal property			(40,083)	(32,526)
Net losses on disposal of real estate	1,124	528	4,293	(1,311)
Net (gain) loss on sale of investments			0	0
Net losses on equity investments			0	0
Deferred income tax			116,099	94,258
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(39,327)	18,799
Inventories			(6,349)	589
Prepaid expenses			112,428	(16,402)
Capitalization of deferred policy acquisition costs			0	0
Other assets			30,337	(2,215)
Related party assets			(20,643)	(16,151)
Accounts payable and accrued expenses			96,269	42,453
Policy benefits and losses, claims and loss expenses payable			10,526	8,353
Other policyholders' funds and liabilities			0	0
Deferred income			5,483	(2,317)
Related party liabilities			749	(956)
Net cash provided by operating activities			1,277,133	872,180
Cash flow from investing activities:
Escrow deposits			(1,978)	7,153
Purchase of:
Property, plant and equipment			(961,995)	(1,917,862)
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			434,860	599,797
Short term investments			0	0
Fixed maturity investments			0	0
Equity securities			0	0
Preferred stock			0
Real estate				311
Mortgage loans			0	0
Net cash used by investing activities			(529,113)	(1,310,601)
Cash flow from financing activities:
Borrowings from credit facilities			780,932	865,362
Principal repayments on credit facilities			(558,280)	(222,832)
Payment of debt issuance costs			(5,020)	(3,671)
Capital lease payments			(173,520)	(247,188)
Employee stock ownership plan shares				(206)
Securitization deposits				(19,600)
Common stock dividends paid			(49,019)
Net contribution from (to) related party			41,199	21,600
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			36,292	393,465
Effects of exchange rate on cash			6,877	5,214
Increase (decrease) in cash and cash equivalents			791,189	(39,742)
Cash and cash equivalents at the beginning of period			459,078	643,918
Cash and cash equivalents at the end of the period	1,250,267	604,176	1,250,267	604,176
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	9,086	7,801	19,217	21,717
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			1,180	1,129
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			(86)	(178)
Net losses on equity investments			669	(3,749)
Deferred income tax			1,685	(1,150)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			5,880	5,931
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			286	1,973
Related party assets			(151)	(1,356)
Accounts payable and accrued expenses			(2,106)	(199)
Policy benefits and losses, claims and loss expenses payable			(8,824)	(6,067)
Other policyholders' funds and liabilities			(5,671)	578
Deferred income			0	0
Related party liabilities			(946)	1,192
Net cash provided by operating activities			11,133	19,821
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(38,789)	(47,036)
Fixed maturity investments			(10,438)	(8,954)
Equity securities			0	0
Preferred stock			0
Real estate			0	(328)
Mortgage loans			(14,780)	(12,750)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			38,830	46,859
Fixed maturity investments			14,217	21,981
Equity securities			0	185
Preferred stock			1,200
Real estate				0
Mortgage loans			879	1,933
Net cash used by investing activities			(8,881)	1,890
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
Securitization deposits				0
Common stock dividends paid			0
Net contribution from (to) related party			0	(21,600)
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			0	(21,600)
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			2,252	111
Cash and cash equivalents at the beginning of period			4,794	5,757
Cash and cash equivalents at the end of the period	7,046	5,868	7,046	5,868
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	7,031	7,395	13,633	16,224
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	6,572	8,046	19,012	20,625
Amortization of premiums and accretion of discounts related to investments, net			9,017	8,719
Amortization of debt issuance costs			0	0
Interest credited to policyholders			38,672	38,169
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			(5,558)	(8,599)
Net losses on equity investments			0	0
Deferred income tax			(759)	(5,303)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(6,052)	29
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(24,903)	(17,530)
Other assets			(503)	(51)
Related party assets			0	0
Accounts payable and accrued expenses			2,988	9,500
Policy benefits and losses, claims and loss expenses payable			12,394	1,688
Other policyholders' funds and liabilities			30,348	(2,701)
Deferred income			1,368
Related party liabilities			(1,369)	210
Net cash provided by operating activities			88,287	60,980
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(1)	(421)
Fixed maturity investments			(341,869)	(258,955)
Equity securities			(838)	(83)
Preferred stock			(16,144)
Real estate			(274)	(156)
Mortgage loans			(77,501)	(30,335)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			0	0
Fixed maturity investments			317,190	171,215
Equity securities			72	0
Preferred stock			0
Real estate				0
Mortgage loans			3,865	7,119
Net cash used by investing activities			(115,500)	(111,616)
Cash flow from financing activities:
Borrowings from credit facilities			9,600	2,500
Principal repayments on credit facilities			(9,788)	(2,500)
Payment of debt issuance costs			0	0
Capital lease payments			0	0
Employee stock ownership plan shares				0
Securitization deposits				0
Common stock dividends paid			0
Net contribution from (to) related party			(18,599)	0
Investment contract deposits			326,055	171,465
Investment contract withdrawals			(169,008)	(122,948)
Net cash provided by (used in) financing activities			138,260	48,517
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			111,047	(2,119)
Cash and cash equivalents at the beginning of period			30,480	24,026
Cash and cash equivalents at the end of the period	141,527	21,907	141,527	21,907
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(16,117)	(15,196)	(32,850)	(37,941)
Earnings from consolidated entities			32,850	37,941
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
Equity securities			0	0
Preferred stock			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
Employee stock ownership plan shares				0
Securitization deposits				0
Common stock dividends paid			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