Debt (Details)	3 Months Ended
Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Fair value	$ 1,741,300,000	$ 1,679,700,000
Debt and Capital Lease Obligations	1,525,500,000	1,528,700,000
Face amount of note convertible into common shares	1,000
Convertible Senior Notes Due 2018
Debt Instrument [Line Items]
Debt	550,000,000	550,000,000
Fair value	735,500,000	689,500,000
Debt and Capital Lease Obligations	$ 548,200,000	547,800,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Number of common shares into which notes are convertible (in shares per one thousand dollar note)	64.3407
Senior Notes Due 2024
Debt Instrument [Line Items]
Debt	$ 400,000,000	400,000,000
Fair value	426,600,000	417,400,000
Debt and Capital Lease Obligations	$ 395,800,000	395,600,000
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt	$ 550,000,000	550,000,000
Fair value	542,400,000	531,900,000
Debt and Capital Lease Obligations	$ 544,700,000	544,600,000
Debt Instrument, Interest Rate, Stated Percentage	3.875%
ESSOP Debt
Debt Instrument [Line Items]
Fair value	$ 4,200,000	8,100,000
Debt and Capital Lease Obligations	$ 4,200,000	$ 8,100,000
Debt, Weighted Average Interest Rate	4.28%	3.98%
Debt [Member]
Debt Instrument [Line Items]
Fair value	$ 32,500,000	$ 32,500,000
Debt and Capital Lease Obligations	$ 32,400,000	$ 32,400,000
Debt, Weighted Average Interest Rate	2.20%	1.90%

The face amount of an individual note that is convertible into a specified number of shares of common stock.

No definition available.

Name:	ori_FaceAmountOfNoteConvertibleIntoCommonShares
Namespace Prefix:	ori_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of equity instruments that the holder of the debt instrument would receive if the debt was converted to equity.

+ References

No definition available.

+ Details

Name:	ori_NumberOfCommonSharesIntoWhichNotesAreConvertible
Namespace Prefix:	ori_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_DebtAndCapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13476-108611

+ Details

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=ori_ConvertibleSeniorNotesDue2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ori_SeniorNotesDue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ori_SeniorNotesDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ori_EssopDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ori_OtherMiscellaneousDebtMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: