Segment Operating Results - Assets by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Assets	$ 1,584,886	$ 1,662,346	$ 1,479,171
United States [Member]
Segment Reporting Information [Line Items]
Assets	1,284,163	1,376,101
Europe and Other [Member]
Segment Reporting Information [Line Items]
Assets	234,984	190,380
Latin America [Member]
Segment Reporting Information [Line Items]
Assets	$ 65,739	$ 95,865