Acquisitions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Transaction	Dec. 31, 2013 Transaction	Dec. 31, 2012
Business Combinations [Abstract]
Revenues from the date of acquisition	$ 23.1	$ 62.1	$ 25.8
Number of transactions	2ddr_NumberOfTransactions	2ddr_NumberOfTransactions

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration