Business Segments (Details 3) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenue	$ 132,871	$ 123,566	$ 133,691	$ 125,032	$ 131,503	$ 124,097	$ 131,161	$ 122,447	$ 515,160	$ 509,208	$ 490,559
United States
Segment Reporting Information [Line Items]
Revenue									344,720	350,632	339,329
United Kingdom
Segment Reporting Information [Line Items]
Revenue									92,059	100,466	93,017
Other Countries
Segment Reporting Information [Line Items]
Revenue									$ 78,381	$ 58,110	$ 58,213