Purchased Intangible Assets and Goodwill (Changes in Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Fair Value Input, Basis Spread on Discount Rate	70
Goodwill [Roll Forward]
Goodwill	$ 169,553	$ 169,553
Accumulated impairment losses	(5,441)	(5,441)
Goodwill, net beginning balance	164,112	164,112
Impairment	(79,700)	0	$ 0
Goodwill, ending balance	169,553	169,553	169,553
Accumulated impairment losses	(85,141)	(5,441)	(5,441)
Goodwill, net ending balance	84,412	164,112	164,112
United States & Canada
Goodwill [Roll Forward]
Goodwill	43,872	43,872
Accumulated impairment losses	(5,441)	(5,441)
Goodwill, net beginning balance	38,431	38,431
Impairment	0	0
Goodwill, ending balance	43,872	43,872	43,872
Accumulated impairment losses	(5,441)	(5,441)	(5,441)
Goodwill, net ending balance	38,431	38,431	38,431
Latin America
Goodwill [Roll Forward]
Goodwill	125,681	125,681
Accumulated impairment losses	0	0
Goodwill, net beginning balance	125,681	125,681
Impairment	(79,700)	0
Goodwill, ending balance	125,681	125,681	125,681
Accumulated impairment losses	(79,700)	0	0
Goodwill, net ending balance	$ 45,981	$ 125,681	$ 125,681
Income Approach Valuation Technique [Member]
Goodwill [Line Items]
Fair Value, Goodwill, Valuation Approach Allocation	70.00%
Market Approach Valuation Technique [Member]
Goodwill [Line Items]
Fair Value, Goodwill, Valuation Approach Allocation	30.00%