Acquisitions (Narrative) (Details) - USD ($) $ in Thousands					6 Months Ended		12 Months Ended
	Nov. 08, 2014	Nov. 07, 2014	Jun. 02, 2014	Nov. 09, 2012	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill					$ 80,360		$ 80,322
Engage Pty Ltd. [Member]
Business Acquisition [Line Items]
Business acquisition, acquisition date				Nov. 09, 2012
Total consideration transferred				$ 10,600
Acquisition costs incurred to acquire entity								$ 500
Assets acquired liabilities assumed, net				800
Potential earn-out consideration				$ 1,700
Change in fair value of contingent consideration					700	$ 200
Synchronite, LLC [Member]
Business Acquisition [Line Items]
Business acquisition, acquisition date			Jun. 02, 2014
Total consideration transferred			$ 4,100
Acquisition costs incurred to acquire entity					400
Assets acquired liabilities assumed, net			45
Potential earn-out consideration			$ 1,800		200
Goodwill					2,700
Intangible assets					1,500
Payments for previous acquisition							1,600
Contact At Once! [Member]
Business Acquisition [Line Items]
Business acquisition, acquisition date		Nov. 07, 2014
Total consideration transferred	$ 67,000
Potential earn-out consideration		$ 4,200
Change in fair value of contingent consideration					$ 3,200
Goodwill		45,100
Intangible assets		20,400
Payments for previous acquisition							$ 200
Cash payment		42,800
Consideration transferred, shares		$ 20,000