Consolidating financial information by industry segment (Cash Flow Statements) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Cash flow from operating activities:
Net earnings	$ 163,542		$ 124,639		$ 291,391		$ 250,846
Earnings from consolidated entities
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation					287,383		269,505
Amortization of deferred policy acquisition costs	5,899		5,944		11,930		12,265
Amortization of debt issuance costs					2,013		1,946
Interest credited to policyholders					17,726		15,119
Change in allowance for losses on trade receivables					309		(2)
Change in allowance for inventory reserves					1,148		2,953
Net gain on sale of real and personal property	(12,036)		(4,938)		(28,331)		(10,026)
Net losses on disposal of real estate	10		(166)		10		181
Net (gain) loss on sale of investments					55		(3,059)
Deferred income tax					89,829		63,065
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables					(14,453)		(15,895)
Inventories					(4,347)		(21,036)
Prepaid expenses					(17,709)		41,486
Capitalization of deferred policy acquisition costs					(12,926)		(15,154)
Other assets					58,139		(10,444)
Related party assets					6,181		8,958
Accounts payable and accrued expenses					63,582		69,550
Policy benefits and losses, claims and loss expenses payable					(49,774)		12,057
Other policyholders' funds and liabilities					3,302		10,305
Deferred income					(124)		3,660
Related party liabilities					(3,276)		(3,662)
Net cash provided by operating activities					702,058		682,618
Cash flow from investing activities:
Escrow deposits					1,362		27,059
Purchase of:
Property, plant and equipment					(1,114,544)		(754,052)
Short term investments					(22,335)		(34,765)
Fixed maturity investments					(239,972)		(219,620)
Equity securities					(957)		(662)
Preferred stock					(81)		(1,000)
Real estate					(218)		(118)
Mortgage loans					(24,132)		(50,817)
Proceeds from sale of:
Property, plant and equipment					429,910		259,450
Short term investments					24,568		38,927
Fixed maturity investments					65,270		70,792
Preferred stock					1,125		988
Real estate							2,664
Mortgage loans					12,912		9,584
Net cash used by investing activities					(867,092)		(651,570)
Cash flow from financing activities:
Borrowings from credit facilities					313,299		285,532
Principal repayments on credit facilities					(182,955)		(214,354)
Payment of debt issuance costs					(1,420)		(3,413)
Capital lease payments					(147,913)		(150,302)
Employee stock ownership plan shares					(137)		(3,960)
Securitization deposits							(186)
Common stock dividends paid					(29,385)		(19,587)
Investment contract deposits					179,608		232,752
Investment contract withdrawals					(71,228)		(97,262)
Net cash provided by (used in) financing activities					59,869		29,220
Effects of exchange rate on cash					(1,783)		10,277
Increase (decrease) in cash and cash equivalents					(106,948)		70,545
Cash and cash equivalents at the beginning of period					759,388		697,806
Cash and cash equivalents at the end of the period	652,440		768,351		652,440		768,351
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Cash flow from operating activities:
Net earnings	163,542		124,639		291,391		250,846
Earnings from consolidated entities					(15,642)		(14,175)
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation					287,383		269,505
Amortization of deferred policy acquisition costs
Amortization of debt issuance costs					2,013		1,946
Interest credited to policyholders
Change in allowance for losses on trade receivables					313		(16)
Change in allowance for inventory reserves					1,148		2,953
Net gain on sale of real and personal property					(28,331)		(10,026)
Net losses on disposal of real estate	10		(166)		10		181
Net (gain) loss on sale of investments
Deferred income tax					89,160		65,587
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables					(14,166)		(21,782)
Inventories					(4,347)		(21,036)
Prepaid expenses					(17,709)		41,486
Capitalization of deferred policy acquisition costs
Other assets					58,539		(11,862)
Related party assets					7,798		6,056
Accounts payable and accrued expenses					49,346		59,671
Policy benefits and losses, claims and loss expenses payable					(54,882)		16,081
Other policyholders' funds and liabilities
Deferred income					(124)		3,660
Related party liabilities					(2,207)		(3,945)
Net cash provided by operating activities					649,693		635,130
Cash flow from investing activities:
Escrow deposits					1,362		27,059
Purchase of:
Property, plant and equipment					(1,114,544)		(754,052)
Short term investments
Fixed maturity investments
Equity securities
Preferred stock
Real estate
Mortgage loans
Proceeds from sale of:
Property, plant and equipment					429,910		259,450
Short term investments
Fixed maturity investments
Preferred stock
Real estate							2,664
Mortgage loans
Net cash used by investing activities					(683,272)		(464,879)
Cash flow from financing activities:
Borrowings from credit facilities					313,299		285,532
Principal repayments on credit facilities					(182,955)		(214,354)
Payment of debt issuance costs					(1,420)		(3,413)
Capital lease payments					(147,913)		(150,302)
Employee stock ownership plan shares					(137)		(3,960)
Securitization deposits							(186)
Common stock dividends paid					(29,385)		(19,587)
Investment contract deposits
Investment contract withdrawals
Net cash provided by (used in) financing activities					(48,511)		(106,270)
Effects of exchange rate on cash					(1,783)		10,277
Increase (decrease) in cash and cash equivalents					(83,873)		74,258
Cash and cash equivalents at the beginning of period					702,036		671,665
Cash and cash equivalents at the end of the period	618,163		745,923		618,163		745,923
Operating Segments [Member] | Property and Casualty Insurance [Member]
Cash flow from operating activities:
Net earnings	6,231	[1]	3,996	[2]	8,399	[3]	7,570	[4]
Earnings from consolidated entities						[5]		[6]
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation						[5]		[6]
Amortization of deferred policy acquisition costs		[1]		[2]		[3]		[4]
Amortization of debt issuance costs						[5]		[6]
Interest credited to policyholders						[5]		[6]
Change in allowance for losses on trade receivables						[5]		[6]
Change in allowance for inventory reserves						[5]		[6]
Net gain on sale of real and personal property						[5]		[6]
Net losses on disposal of real estate		[1]		[2]		[3]		[4]
Net (gain) loss on sale of investments					(66)	[5]	(748)	[6]
Deferred income tax					1,228	[5]	(1,730)	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables					1,151	[5]	6,281	[6]
Inventories						[5]		[6]
Prepaid expenses						[5]		[6]
Capitalization of deferred policy acquisition costs						[5]		[6]
Other assets					80	[5]	1,563	[6]
Related party assets					(1,617)	[5]	2,902	[6]
Accounts payable and accrued expenses					1,106	[5]	3,282	[6]
Policy benefits and losses, claims and loss expenses payable					1,166	[5]	(5,604)	[6]
Other policyholders' funds and liabilities					14	[5]	5,685	[6]
Deferred income						[5]		[6]
Related party liabilities					(453)	[5]	292	[6]
Net cash provided by operating activities					11,008	[5]	19,493	[6]
Cash flow from investing activities:
Escrow deposits						[5]		[6]
Purchase of:
Property, plant and equipment						[5]		[6]
Short term investments					(22,092)	[5]	(27,059)	[6]
Fixed maturity investments					(17,588)	[5]	(29,381)	[6]
Equity securities						[5]		[6]
Preferred stock						[5]	(1,000)	[6]
Real estate					(144)	[5]		[6]
Mortgage loans					(4,612)	[5]	(7,609)	[6]
Proceeds from sale of:
Property, plant and equipment						[5]		[6]
Short term investments					24,568	[5]	28,879	[6]
Fixed maturity investments					7,921	[5]	12,033	[6]
Preferred stock					1,125	[5]	988	[6]
Real estate						[5]		[6]
Mortgage loans					422	[5]	1,722	[6]
Net cash used by investing activities					(10,400)	[5]	(21,427)	[6]
Cash flow from financing activities:
Borrowings from credit facilities						[5]		[6]
Principal repayments on credit facilities						[5]		[6]
Payment of debt issuance costs						[5]		[6]
Capital lease payments						[5]		[6]
Employee stock ownership plan shares						[5]		[6]
Securitization deposits						[5]		[6]
Common stock dividends paid						[5]		[6]
Investment contract deposits						[5]		[6]
Investment contract withdrawals						[5]		[6]
Net cash provided by (used in) financing activities						[5]		[6]
Effects of exchange rate on cash						[5]		[6]
Increase (decrease) in cash and cash equivalents					608	[5]	(1,934)	[6]
Cash and cash equivalents at the beginning of period					6,639	[7]	12,725	[6]
Cash and cash equivalents at the end of the period	7,247	[8]	10,791	[6]	7,247	[8]	10,791	[6]
Operating Segments [Member] | Life Insurance [Member]
Cash flow from operating activities:
Net earnings	5,755	[1]	4,369	[2]	7,243	[3]	6,605	[4]
Earnings from consolidated entities						[5]		[6]
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation						[5]		[6]
Amortization of deferred policy acquisition costs	5,899	[1]	5,944	[2]	11,930	[3]	12,265	[4]
Amortization of debt issuance costs						[5]		[6]
Interest credited to policyholders					17,726	[5]	15,119	[6]
Change in allowance for losses on trade receivables					(4)	[5]	14	[6]
Change in allowance for inventory reserves						[5]		[6]
Net gain on sale of real and personal property						[5]		[6]
Net losses on disposal of real estate		[1]		[2]		[3]		[4]
Net (gain) loss on sale of investments					121	[5]	(2,311)	[6]
Deferred income tax					(559)	[5]	(792)	[6]
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables					(1,438)	[5]	(394)	[6]
Inventories						[5]		[6]
Prepaid expenses						[5]		[6]
Capitalization of deferred policy acquisition costs					(12,926)	[5]	(15,154)	[6]
Other assets					(480)	[5]	(145)	[6]
Related party assets						[5]		[6]
Accounts payable and accrued expenses					13,130	[5]	6,597	[6]
Policy benefits and losses, claims and loss expenses payable					3,942	[5]	1,580	[6]
Other policyholders' funds and liabilities					3,288	[5]	4,620	[6]
Deferred income						[5]		[6]
Related party liabilities					(616)	[5]	(9)	[6]
Net cash provided by operating activities					41,357	[5]	27,995	[6]
Cash flow from investing activities:
Escrow deposits						[5]		[6]
Purchase of:
Property, plant and equipment						[5]		[6]
Short term investments					(243)	[5]	(7,706)	[6]
Fixed maturity investments					(222,384)	[5]	(190,239)	[6]
Equity securities					(957)	[5]	(662)	[6]
Preferred stock					(81)	[5]		[6]
Real estate					(74)	[5]	(118)	[6]
Mortgage loans					(19,520)	[5]	(43,208)	[6]
Proceeds from sale of:
Property, plant and equipment						[5]		[6]
Short term investments						[5]	10,048	[6]
Fixed maturity investments					57,349	[5]	58,759	[6]
Preferred stock						[5]		[6]
Real estate						[5]		[6]
Mortgage loans					12,490	[5]	7,862	[6]
Net cash used by investing activities					(173,420)	[5]	(165,264)	[6]
Cash flow from financing activities:
Borrowings from credit facilities						[5]		[6]
Principal repayments on credit facilities						[5]		[6]
Payment of debt issuance costs						[5]		[6]
Capital lease payments						[5]		[6]
Employee stock ownership plan shares						[5]		[6]
Securitization deposits						[5]		[6]
Common stock dividends paid						[5]		[6]
Investment contract deposits					179,608	[5]	232,752	[6]
Investment contract withdrawals					(71,228)	[5]	(97,262)	[6]
Net cash provided by (used in) financing activities					108,380	[5]	135,490	[6]
Effects of exchange rate on cash						[5]		[6]
Increase (decrease) in cash and cash equivalents					(23,683)	[5]	(1,779)	[6]
Cash and cash equivalents at the beginning of period					50,713	[7]	13,416	[6]
Cash and cash equivalents at the end of the period	27,030	[8]	11,637	[6]	27,030	[8]	11,637	[6]
Consolidation, Eliminations [Member]
Cash flow from operating activities:
Net earnings	(11,986)		(8,365)		(15,642)		(14,175)
Earnings from consolidated entities					15,642		14,175
Adjustments to reconcile net earnings to cash provided by operations:
Depreciation
Amortization of deferred policy acquisition costs
Amortization of debt issuance costs
Interest credited to policyholders
Change in allowance for losses on trade receivables
Change in allowance for inventory reserves
Net gain on sale of real and personal property
Net losses on disposal of real estate
Net (gain) loss on sale of investments
Deferred income tax
Net change in other operating assets and liabilities:
Reinsurance recoverables and trade receivables
Inventories
Prepaid expenses
Capitalization of deferred policy acquisition costs
Other assets
Related party assets
Accounts payable and accrued expenses
Policy benefits and losses, claims and loss expenses payable
Other policyholders' funds and liabilities
Deferred income
Related party liabilities
Net cash provided by operating activities
Cash flow from investing activities:
Escrow deposits
Purchase of:
Property, plant and equipment
Short term investments
Fixed maturity investments
Equity securities
Preferred stock
Real estate
Mortgage loans
Proceeds from sale of:
Property, plant and equipment
Short term investments
Fixed maturity investments
Preferred stock
Real estate
Mortgage loans
Net cash used by investing activities
Cash flow from financing activities:
Borrowings from credit facilities
Principal repayments on credit facilities
Payment of debt issuance costs
Capital lease payments
Employee stock ownership plan shares
Securitization deposits
Common stock dividends paid
Investment contract deposits
Investment contract withdrawals
Net cash provided by (used in) financing activities
Effects of exchange rate on cash
Increase (decrease) in cash and cash equivalents
Cash and cash equivalents at the beginning of period
Cash and cash equivalents at the end of the period

[1] Balances for the quarter ended June 30, 2018

[2] Balances for the quarter ended June 30, 2017

[3] Balances for the six months ended June 30, 2018

[4] Balances for the six months ended June 30, 2017

[5] Balance for the period ended June 30, 2018

[6] Balance for the period ended June 30, 2017

[7] Balances as of December 31, 2017

[8] Balances as of June 30, 2018