Acquisitions and Dispositions - Deny Designs (Details) shares in Thousands, $ in Thousands		12 Months Ended
	May 01, 2017 USD ($) installment shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Allocation of the purchase price
Goodwill		$ 17,152	$ 11,167	$ 10,358
Deny Designs
Acquisitions
Total consideration	$ 12,000
Purchase consideration, cash	$ 6,700
Purchase consideration, common stock, shares | shares	215
Purchase consideration, common stock, value	$ 1,700
Contingent consideration	$ 3,600
Number of annual installments | installment	3
Allocation of the purchase price
Goodwill	$ 5,906
Other assets and liabilities assumed	705
Total purchase consideration	11,161
Weighted average useful life		7 years
Contingent consideration
Contingent consideration	2,800
Maximum contingent consideration	3,600
Fair value adjustment		$ 300
Deny Designs | Contingent Consideration, Payable in First Year
Contingent consideration
Minimum contingent consideration	300	300
Maximum contingent consideration	1,200	1,200
Deny Designs | Contingent Consideration, Payable in Second Year
Contingent consideration
Minimum contingent consideration		300
Maximum contingent consideration		1,200
Deny Designs | Contingent Consideration, Payable in Third Year
Contingent consideration
Minimum contingent consideration		300
Maximum contingent consideration		$ 1,200
Deny Designs | Trademark
Allocation of the purchase price
Intangibles	2,300
Intangibles, useful life		10 years
Deny Designs | Customer relationships
Allocation of the purchase price
Intangibles	1,400
Intangibles, useful life		5 years
Deny Designs | Artist relationships
Allocation of the purchase price
Intangibles	300
Intangibles, useful life		3 years
Deny Designs | Technology
Allocation of the purchase price
Intangibles	$ 550
Intangibles, useful life		3 years