Business Acquisitions (Details) - USD ($) $ in Thousands	Sep. 15, 2017	Sep. 07, 2016	Oct. 01, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill				$ 51,438	$ 48,678	$ 47,396
Veri
Business Acquisition [Line Items]
Total purchase price	$ 3,500
Cash paid for acquisitions and investments	3,200
Consideration, amount of holdback	$ 300
Consideration holdback period	18 months
Goodwill				2,800
How He Asked
Business Acquisition [Line Items]
Total purchase price		$ 1,500
Cash paid for acquisitions and investments		1,400
Consideration, amount of holdback		$ 100
Consideration holdback period		12 months
Goodwill		$ 1,300
GigMasters.com
Business Acquisition [Line Items]
Total purchase price			$ 7,868
Cash paid for acquisitions and investments			6,100
Finite-lived intangible assets			3,700
Goodwill			$ 5,525
Previous equity interest in acquiree			28.70%
Interest acquired			71.30%
Equity interest in acquiree, remeasurement gain			$ 800
Portion allocated to tangible assets			500
Technology assets | Veri
Business Acquisition [Line Items]
Finite-lived intangible assets				$ 700
Trade names | How He Asked
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 200
Trade names | GigMasters.com
Business Acquisition [Line Items]
Finite-lived intangible assets			$ 480