Segment Information - Revenues Attributable To Domestic And Foreign Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 222,779	$ 239,012	$ 209,931
Total Americas [Member]
Segment Reporting Information [Line Items]
Revenue	153,551	171,835	149,041
United States [Member]
Segment Reporting Information [Line Items]
Revenue	146,733	159,539	138,533
Other Americas [Member]
Segment Reporting Information [Line Items]
Revenue	6,818	12,296	10,508
EMEA [Member]
Segment Reporting Information [Line Items]
Revenue	50,511	51,548	44,506
APAC [Member]
Segment Reporting Information [Line Items]
Revenue	18,717	15,629	$ 16,384
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenue	$ 35,300	$ 38,200