Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Cash flow from operating activities:
Net earnings	$ 30,932	$ 78,635	$ 319,680	$ 370,026
Earnings from consolidated entities			0	0
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			494,753	431,652
Amortization of deferred policy acquisition costs	8,046	6,654	20,625	18,584
Amortization of premiums and accretion of discounts related to investments, net			9,848	9,802
Amortization of debt issuance costs			3,275	2,922
Interest credited to policyholders			38,169	28,540
Change in allowance for losses on trade receivables			(76)	124
Change in allowance for inventory reserves			(85)	2,539
Net gain on sale of real and personal property	(2,151)	796	(32,526)	(29,127)
Net losses on disposal of real estate	528	0	(1,311)	10
Net (gain) loss on sale of investments			(8,777)	(3,594)
Net losses on equity investments			(3,749)	4,289
Deferred income tax			87,805	104,325
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			24,759	1,601
Inventories			589	(8,858)
Prepaid expenses			(16,402)	(12,533)
Capitalization of deferred policy acquisition costs			(17,530)	(19,994)
Other assets			(293)	159,125
Related party assets			(17,507)	(1,838)
Accounts payable and accrued expenses			51,754	(14,231)
Policy benefits and losses, claims and loss expenses payable			3,974	(159,285)
Other policyholders' funds and liabilities			(2,123)	2,867
Deferred income			(2,317)	(4,982)
Related party liabilities			446	(3,269)
Net cash provided by operating activities			952,981	878,695
Cash flow from investing activities:
Escrow deposits			7,153	(3,292)
Purchase of:
Property, plant and equipment			(1,917,862)	(1,325,365)
Short term investments			(47,457)	(39,494)
Fixed maturity investments			(267,909)	(394,266)
Equity securities			(83)	(957)
Preferred stock			0	(81)
Real estate			(484)	(505)
Mortgage loans			(43,085)	(56,892)
Proceeds from sale of:
Property, plant and equipment			599,797	561,848
Short term investments			46,859	47,012
Fixed maturity investments			193,196	82,776
Equity securities			185	8,608
Real estate			311	0
Mortgage loans			9,052	116,800
Net cash used by investing activities			(1,420,327)	(1,002,183)
Cash flow from financing activities:
Borrowings from credit facilities			867,862	693,132
Principal repayments on credit facilities			(225,332)	(255,123)
Payment of debt issuance costs			(3,671)	(5,097)
Capital lease payments			(247,188)	(236,683)
Employee stock ownership plan shares			(206)	(203)
Securitization deposits				(29,385)
Common stock dividends paid			(19,600)	(29,385)
Proceeds from Contributions from Affiliates			0
Investment contract deposits			171,465	300,920
Investment contract withdrawals			(122,948)	(109,641)
Net cash provided by (used in) financing activities			420,382	357,920
Effects of exchange rate on cash			5,214	(9,435)
Increase (decrease) in cash and cash equivalents			(41,750)	224,997
Cash and cash equivalents at the beginning of period			673,701	759,388
Cash and cash equivalents at the end of the period	631,951	984,385	631,951	984,385
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	30,932	78,635	319,680	370,026
Earnings from consolidated entities			(37,941)	(30,306)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation			494,753	431,652
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			3,275	2,922
Interest credited to policyholders			0
Change in allowance for losses on trade receivables			(76)	129
Change in allowance for inventory reserves			(85)	2,539
Net gain on sale of real and personal property			(32,526)	(29,127)
Net losses on disposal of real estate	528		(1,311)	10
Net (gain) loss on sale of investments			0	0
Net losses on equity investments			0	0
Deferred income tax			94,258	108,618
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			18,799	2,323
Inventories			589	(8,858)
Prepaid expenses			(16,402)	(12,533)
Capitalization of deferred policy acquisition costs			0	0
Other assets			(2,215)	159,232
Related party assets			(16,151)	(1,428)
Accounts payable and accrued expenses			42,453	(16,639)
Policy benefits and losses, claims and loss expenses payable			8,353	(157,470)
Other policyholders' funds and liabilities			0	0
Deferred income			(2,317)	(4,982)
Related party liabilities			(956)	(3,039)
Net cash provided by operating activities			872,180	813,069
Cash flow from investing activities:
Escrow deposits			7,153	(3,292)
Purchase of:
Property, plant and equipment			(1,917,862)	(1,325,365)
Short term investments			0	0
Fixed maturity investments			0	0
Equity securities			0	0
Preferred stock				0
Real estate			0	(236)
Mortgage loans			0	0
Proceeds from sale of:
Property, plant and equipment			599,797	561,848
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			(1,310,601)	(767,045)
Cash flow from financing activities:
Borrowings from credit facilities			865,362	666,232
Principal repayments on credit facilities			(222,832)	(228,223)
Payment of debt issuance costs			(3,671)	(5,097)
Capital lease payments			(247,188)	(236,683)
Employee stock ownership plan shares			(206)	(203)
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			393,465	166,641
Effects of exchange rate on cash			5,214	(9,435)
Increase (decrease) in cash and cash equivalents			(39,742)	203,230
Cash and cash equivalents at the beginning of period			643,918	702,036
Cash and cash equivalents at the end of the period	604,176	905,266	604,176	905,266
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	7,801	8,815	21,717	17,214
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			1,129	991
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
Net (gain) loss on sale of investments			(178)	(3,007)
Net losses on equity investments			(3,749)	4,289
Deferred income tax			(1,150)	(665)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			5,931	2,000
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			0	0
Other assets			1,973	391
Related party assets			(1,356)	(410)
Accounts payable and accrued expenses			(199)	1,174
Policy benefits and losses, claims and loss expenses payable			(6,067)	(4,751)
Other policyholders' funds and liabilities			578	(327)
Deferred income			0	0
Related party liabilities			1,192	318
Net cash provided by operating activities			19,821	17,217
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(47,036)	(39,251)
Fixed maturity investments			(8,954)	(32,862)
Equity securities			0	0
Preferred stock				0
Real estate			(328)	(187)
Mortgage loans			(12,750)	(13,312)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			46,859	47,012
Fixed maturity investments			21,981	8,895
Equity securities			185	8,608
Preferred stock				1,625
Real estate			0
Mortgage loans			1,933	1,331
Net cash used by investing activities			1,890	(18,141)
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			(21,600)
Investment contract deposits			0	0
Investment contract withdrawals			0	0
Net cash provided by (used in) financing activities			(21,600)	0
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			111	(924)
Cash and cash equivalents at the beginning of period			5,757	6,639
Cash and cash equivalents at the end of the period	5,868	5,715	5,868	5,715
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	7,395	5,849	16,224	13,092
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	8,046	6,654	20,625	18,584
Amortization of premiums and accretion of discounts related to investments, net			8,719	8,811
Amortization of debt issuance costs			0	0
Interest credited to policyholders			38,169	28,540
Change in allowance for losses on trade receivables			0	(5)
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
Net (gain) loss on sale of investments			(8,599)	(587)
Net losses on equity investments			0	0
Deferred income tax			(5,303)	(3,628)
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables			29	(2,722)
Inventories			0	0
Prepaid expenses			0	0
Capitalization of deferred policy acquisition costs			(17,530)	(19,994)
Other assets			(51)	(498)
Related party assets			0	0
Accounts payable and accrued expenses			9,500	1,234
Policy benefits and losses, claims and loss expenses payable			1,688	2,936
Other policyholders' funds and liabilities			(2,701)	3,194
Deferred income			0
Related party liabilities			210	(548)
Net cash provided by operating activities			60,980	48,409
Cash flow from investing activities:
Escrow deposits			0	0
Purchase of:
Property, plant and equipment			0	0
Short term investments			(421)	(243)
Fixed maturity investments			(258,955)	(361,404)
Equity securities			(83)	(957)
Preferred stock				(81)
Real estate			(156)	(82)
Mortgage loans			(30,335)	(43,580)
Proceeds from sale of:
Property, plant and equipment			0	0
Short term investments			0	0
Fixed maturity investments			171,215	73,881
Equity securities			0	0
Preferred stock				0
Real estate			0
Mortgage loans			7,119	115,469
Net cash used by investing activities			(111,616)	(216,997)
Cash flow from financing activities:
Borrowings from credit facilities			2,500	26,900
Principal repayments on credit facilities			(2,500)	(26,900)
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			171,465	300,920
Investment contract withdrawals			(122,948)	(109,641)
Net cash provided by (used in) financing activities			48,517	191,279
Effects of exchange rate on cash			0	0
Increase (decrease) in cash and cash equivalents			(2,119)	22,691
Cash and cash equivalents at the beginning of period			24,026	50,713
Cash and cash equivalents at the end of the period	21,907	73,404	21,907	73,404
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(15,196)	(14,664)	(37,941)	(30,306)
Earnings from consolidated entities			37,941	30,306
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
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	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