Acquisitions (Components of Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified			6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended
Nov. 09, 2012	Jun. 30, 2013 Engage Pty Ltd. [Member]	Jun. 30, 2013 Technology [Member]	Dec. 31, 2012 Technology [Member]	Jun. 30, 2013 Technology [Member] Engage Pty Ltd. [Member]	Jun. 30, 2013 Trade Names [Member]	Dec. 31, 2012 Trade Names [Member]	Jun. 30, 2013 Trade Names [Member] Engage Pty Ltd. [Member]	Jun. 30, 2013 Customer Relationships [Member] Engage Pty Ltd. [Member]	Jun. 30, 2013 Non-compete Agreements [Member]	Dec. 31, 2012 Non-compete Agreements [Member]	Jun. 30, 2013 Non-compete Agreements [Member] Engage Pty Ltd. [Member]
Business Acquisition [Line Items]
Intangible assets	$ 3,600	$ 3,600			$ 768			$ 95	$ 2,661			$ 76
Weighted average useful life			3 years 9 months 18 days	3 years 9 months 18 days	36 months	2 years 8 months 12 days	2 years 8 months 12 days	12 months	48 months	1 year 2 months 12 days	1 year 2 months 12 days	12 months

The amount of acquisition cost of a business combination allocated to an identifiable intangible asset that will be amortized.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationAmortizableIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant