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Fair Value Measurements - Summary of Placement in the Fair Value Hierarchy of Financial Assets that are Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets
Assets, Fair Value Disclosure	$ 387,188us-gaap_AssetsFairValueDisclosure	$ 280,497us-gaap_AssetsFairValueDisclosure
U.S. government debt securities
Assets
Assets, Fair Value Disclosure	91,238us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember	115,335us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember
Equity Securities
Assets
Assets, Fair Value Disclosure	294,922us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember	164,889us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember
Other Financial Assets
Assets
Assets, Fair Value Disclosure	1,028us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember	273us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember
Quoted Prices in Active Markets (Level 1)
Assets
Assets, Fair Value Disclosure	277,903us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member	143,927us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Quoted Prices in Active Markets (Level 1) | U.S. government debt securities
Assets
Assets, Fair Value Disclosure	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Quoted Prices in Active Markets (Level 1) | Equity Securities
Assets
Assets, Fair Value Disclosure	277,903us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member	143,927us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Quoted Prices in Active Markets (Level 1) | Other Financial Assets
Assets
Assets, Fair Value Disclosure	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Significant Other Observable Inputs (Level 2)
Assets
Assets, Fair Value Disclosure	109,285us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	136,570us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Significant Other Observable Inputs (Level 2) | U.S. government debt securities
Assets
Assets, Fair Value Disclosure	91,238us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	115,335us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Significant Other Observable Inputs (Level 2) | Equity Securities
Assets
Assets, Fair Value Disclosure	17,019us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	20,962us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Significant Other Observable Inputs (Level 2) | Other Financial Assets
Assets
Assets, Fair Value Disclosure	1,028us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	273us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Significant Unobservable Inputs (Level 3)
Assets
Assets, Fair Value Disclosure	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Significant Unobservable Inputs (Level 3) | U.S. government debt securities
Assets
Assets, Fair Value Disclosure	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_USGovernmentDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Significant Unobservable Inputs (Level 3) | Equity Securities
Assets
Assets, Fair Value Disclosure	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member	0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Significant Unobservable Inputs (Level 3) | Other Financial Assets
Assets
Assets, Fair Value Disclosure	$ 0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member	$ 0us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByAssetClassAxis = xon_OtherFinancialAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member

X

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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