v2.4.0.8

Fair Value Measurements - Summary of Placement in the Fair Value Hierarchy of Financial Assets that are Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012 | Dec. 31, 2011
--- | --- | --- | ---
Assets |  |  |
Fair value of assets | $ 325,348 | $ 83,376 | $ 39,097
Equity Securities [Member] |  |  |
Assets |  |  |
Fair value of assets | 107,567 | 83,116 | 39,097
Certificates of Deposit [Member] |  |  |
Assets |  |  |
Fair value of assets | 1,766 | 260 |
US Government Debt Securities [Member] |  |  |
Assets |  |  |
Fair value of assets | 205,768 |  |
Commercial Paper [Member] |  |  |
Assets |  |  |
Fair value of assets | 10,247 |  |
Scenario, Previously Reported [Member] |  |  |
Assets |  |  |
Fair value of assets |  | 83,116 |
Quoted Prices in Active Markets (Level 1) [Member] |  |  |
Assets |  |  |
Fair value of assets | 75,754 | 72,988 | 39,097
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member] |  |  |
Assets |  |  |
Fair value of assets | 75,754 | 72,988 | 39,097
Quoted Prices in Active Markets (Level 1) [Member] | Certificates of Deposit [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Quoted Prices in Active Markets (Level 1) [Member] | US Government Debt Securities [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Quoted Prices in Active Markets (Level 1) [Member] | Commercial Paper [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Quoted Prices in Active Markets (Level 1) [Member] | Scenario, Previously Reported [Member] |  |  |
Assets |  |  |
Fair value of assets |  | 72,988 |
Significant Other Observable Inputs (Level 2) [Member] |  |  |
Assets |  |  |
Fair value of assets | 249,594 | 10,388 |
Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member] |  |  |
Assets |  |  |
Fair value of assets | 31,813 | 10,128 |
Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member] |  |  |
Assets |  |  |
Fair value of assets | 1,766 | 260 |
Significant Other Observable Inputs (Level 2) [Member] | US Government Debt Securities [Member] |  |  |
Assets |  |  |
Fair value of assets | 205,768 |  |
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member] |  |  |
Assets |  |  |
Fair value of assets | 10,247 |  |
Significant Other Observable Inputs (Level 2) [Member] | Scenario, Previously Reported [Member] |  |  |
Assets |  |  |
Fair value of assets |  | 10,128 |
Significant Unobservable Inputs (Level 3) [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Significant Unobservable Inputs (Level 3) [Member] | Certificates of Deposit [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Significant Unobservable Inputs (Level 3) [Member] | US Government Debt Securities [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |
Significant Unobservable Inputs (Level 3) [Member] | Commercial Paper [Member] |  |  |
Assets |  |  |
Fair value of assets |  |  |

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- 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=25499696&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration