Revenue Recognition (Revenue by Market Group) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 927,740	$ 913,219		$ 900,423
UMG [Member]
Disaggregation of Revenue [Line Items]
Revenue	733,663	730,482	[1]	750,007	[1]
IMG [Member]
Disaggregation of Revenue [Line Items]
Revenue	193,632	181,948	[1]	147,147	[1]
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 445	$ 789	[1]	$ 3,269	[1]

[1] Due to the market group changes discussed above, we have recast our revenue by market group for the years ended December 31, 2020 and 2019 to present them on a consistent basis with the current year.