Income Taxes (Summary of Changes in Gross Amount of Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized tax benefits
Unrealized tax benefit, beginning balance	$ 31,475	$ 33,766	$ 35,388
Additions based on tax positions related to the current year	4,795	4,627	3,550
Additions based on tax positions related to prior years	0	0	4,255
Payments related to items settled with taxing authorities	0	(443)	(2,792)
Reduction due to lapse of statute of limitations and settlements	(5,303)	(6,475)	(6,635)
Unrealized tax benefit, ending balance	$ 30,967	$ 31,475	$ 33,766