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Related party transactions and balances - Summary of Related Party Transactions (Detail) (Advertising [Member], USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Advertising [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Revenue from provision of advertising services | $ 32 | $ 45 | $ 55
Expenses for leases of advertising space |  |  | $ 643

X
- Definition Related Party Transaction Rent Expenses For Lease + References No definition available. + Details
Name: | idi_RelatedPartyTransactionRentExpensesForLease
Namespace Prefix: | idi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration