Business Combinations - Plain Vanilla, Inc. (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 19, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets acquired:
Goodwill	$ 116,832		$ 87,890	$ 87,964
Plain Vanilla Corp.
Business Acquisition [Line Items]
Principal amount of investment		$ 7,500
Fair value of investment		3,200
Assets acquired:
Cash		1,200
Accounts receivable		183
Intangible assets		1,817
Total assets acquired		3,200
Goodwill		0
Titles, content and technology | Plain Vanilla Corp.
Assets acquired:
Intangible assets		$ 1,817