Segment Information (Schedule of Revenue by Geographic Region) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenues	$ 1,032,327	$ 1,034,480	$ 919,486
United States [Member]
Segment Reporting Information [Line Items]
Total revenues	931,649	938,224	833,527
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total revenues	50,700	55,626	62,099
Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 49,978	$ 40,630	$ 23,860