Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Cash flow from operating activities:
Net earnings	$ 156,326	$ 163,542	$ 288,748	$ 291,391
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			326,830	287,383
Amortization of deferred policy acquisition costs	6,515	5,899	12,579	11,930
Amortization of premiums and accretion of discounts related to investments, net			6,481	6,457
Amortization of debt issuance costs			2,100	2,013
Interest credited to policyholders			26,584	17,726
Change in allowance for losses on trade receivables			(113)	309
Change in allowance for inventory reserves			537	1,148
Net gain on sale of real and personal property			(34,677)	(28,331)
Net losses on disposal of real estate	(217)	10	(1,839)	10
Net (gain) loss on sale of investments			(7,595)	55
Net losses on equity investments			(2,553)	1,344
Deferred income tax			83,708	88,485
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			2,471	(14,453)
Inventories			613	(4,347)
Prepaid expenses			(21,908)	(17,709)
Capitalization of deferred policy acquisition costs			(10,370)	(12,926)
Other assets			525	58,139
Related party assets			(5,019)	6,181
Accounts payable and accrued expenses			60,587	57,744
Policy benefits and losses, claims and loss expenses payable			10,709	(49,774)
Other policyholders' funds and liabilities			(4,136)	3,302
Deferred income			2,077	(124)
Related party liabilities			1,425	(3,276)
Net cash provided by operating activities			737,764	702,677
Cash flow from investing activities:
Escrow deposits			5,573	1,362
Purchase of:
Property, plant and equipment			(1,589,371)	(1,114,544)
Short term investments			(20,380)	(22,335)
Fixed maturity investments			(178,626)	(239,972)
Equity securities			(83)	(957)
Preferred stock			0	(81)
Real estate			(368)	(218)
Mortgage loans			(19,660)	(24,132)
Proceeds from sale of:
Property, plant and equipment			401,451	429,910
Short term investments			17,282	24,568
Fixed maturity investments			127,683	64,651
Preferred stock			0	1,125
Real estate			311
Mortgage loans			4,299	12,912
Net cash used by investing activities			(1,251,889)	(867,711)
Cash flow from financing activities:
Borrowings from credit facilities			658,745	313,299
Principal repayments on credit facilities			(143,634)	(182,955)
Payment of debt issuance costs			(2,301)	(1,420)
Capital lease payments			(180,902)	(147,913)
Employee stock ownership plan shares			(206)	(137)
Securitization deposits				(29,385)
Common stock dividends paid			(19,600)	(29,385)
Proceeds from Contributions from Affiliates			21,600	0
Investment contract deposits			105,846	179,608
Investment contract withdrawals			(78,177)	(71,228)
Net cash provided by (used in) financing activities			361,371	59,869
Effects of exchange rate on cash			4,284	(1,783)
Increase (decrease) in cash and cash equivalents			(148,470)	(106,948)
Cash and cash equivalents at the beginning of period			673,701	759,388
Cash and cash equivalents at the end of the period	525,231	652,440	525,231	652,440
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	156,326	163,542	288,748	291,391
Earnings from consolidated entities			(22,745)	(15,642)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			326,830	287,383
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			2,100	2,013
Interest credited to policyholders			0	0
Change in allowance for losses on trade receivables			(113)	313
Change in allowance for inventory reserves			537	1,148
Net gain on sale of real and personal property			(34,677)	(28,331)
Net losses on disposal of real estate	(217)	10	(1,839)	10
Net (gain) loss on sale of investments			0
Net losses on equity investments			0	0
Deferred income tax			87,544	89,160
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(987)	(14,166)
Inventories			613	(4,347)
Prepaid expenses			(21,908)	(17,709)
Capitalization of deferred policy acquisition costs			0	0
Other assets			(1,205)	58,539
Related party assets			(2,628)	7,798
Accounts payable and accrued expenses			59,091	49,346
Policy benefits and losses, claims and loss expenses payable			17,272	(54,882)
Other policyholders' funds and liabilities			0	0
Deferred income			2,077	(124)
Related party liabilities			406	(2,207)
Net cash provided by operating activities			699,116	649,693
Cash flow from investing activities:
Escrow deposits			5,573	1,362
Purchase of:
Property, plant and equipment			(1,589,371)	(1,114,544)
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			401,451	429,910
Short term investments			0	0
Fixed maturity investments			0	0
Real estate			311	0
Mortgage loans			0	0
Net cash used by investing activities			(1,182,036)	(683,272)
Cash flow from financing activities:
Borrowings from credit facilities			656,245	313,299
Principal repayments on credit facilities			(141,134)	(182,955)
Payment of debt issuance costs			(2,301)	(1,420)
Capital lease payments			(180,902)	(147,913)
Employee stock ownership plan shares			(206)	(137)
Securitization deposits				(29,385)
Common stock dividends paid			(19,600)
Proceeds from Contributions from Affiliates			21,600
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			333,702	(48,511)
Effects of exchange rate on cash			4,284	(1,783)
Increase (decrease) in cash and cash equivalents			(144,934)	(83,873)
Cash and cash equivalents at the beginning of period			643,918	702,036
Cash and cash equivalents at the end of the period	498,984	618,163	498,984	618,163
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	7,228	6,231	13,916	8,399
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			754	619
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			(127)	(66)
Net losses on equity investments			(2,553)	1,344
Deferred income tax			(1,438)	(116)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			5,430	1,151
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			1,736	80
Related party assets			(2,391)	(1,617)
Accounts payable and accrued expenses			11	1,106
Policy benefits and losses, claims and loss expenses payable			(6,214)	1,166
Other policyholders' funds and liabilities			381	14
Deferred income			0	0
Related party liabilities			412	(453)
Net cash provided by operating activities			9,917	11,627
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(20,275)	(22,092)
Fixed maturity investments			(6,531)	(17,588)
Equity securities			0	0
Preferred stock				0
Real estate			(328)	(144)
Mortgage loans			(6,250)	(4,612)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			17,282	24,568
Fixed maturity investments			10,308	7,302
Real estate			0	1,125
Mortgage loans			1,696	422
Net cash used by investing activities			(4,098)	(11,019)
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
Proceeds from Contributions from Affiliates			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			5,819	608
Cash and cash equivalents at the beginning of period			5,757	6,639
Cash and cash equivalents at the end of the period	11,576	7,247	11,576	7,247
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	5,686	5,755	8,829	7,243
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	6,515	5,899	12,579	11,930
Amortization of premiums and accretion of discounts related to investments, net			5,727	5,838
Amortization of debt issuance costs			0	0
Interest credited to policyholders			26,584	17,726
Change in allowance for losses on trade receivables			0	(4)
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			(7,468)	121
Net losses on equity investments			0	0
Deferred income tax			(2,398)	(559)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			(1,972)	(1,438)
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(10,370)	(12,926)
Other assets			(6)	(480)
Related party assets			0	0
Accounts payable and accrued expenses			1,485	7,292
Policy benefits and losses, claims and loss expenses payable			(349)	3,942
Other policyholders' funds and liabilities			(4,517)	3,288
Deferred income			0	0
Related party liabilities			607	(616)
Net cash provided by operating activities			28,731	41,357
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(105)	(243)
Fixed maturity investments			(172,095)	(222,384)
Equity securities			(83)	(957)
Preferred stock				(81)
Real estate			(40)	(74)
Mortgage loans			(13,410)	(19,520)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			0	0
Fixed maturity investments			117,375	57,349
Real estate			0	0
Mortgage loans			2,603	12,490
Net cash used by investing activities			(65,755)	(173,420)
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
Proceeds from Contributions from Affiliates			0
Investment contract deposits			105,846	179,608
Investment contract withdrawals			(78,177)	(71,228)
Net cash provided by (used in) financing activities			27,669	108,380
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			(9,355)	(23,683)
Cash and cash equivalents at the beginning of period			24,026	50,713
Cash and cash equivalents at the end of the period	14,671	27,030	14,671	27,030
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(12,914)	(11,986)	(22,745)	(15,642)
Earnings from consolidated entities			22,745	15,642
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
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
Proceeds from Contributions from Affiliates			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