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Revenue From Contracts With Customers (Changes in Contract Assets and Contract Liabilities) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Contract assets        
Contract assets $ 7,670 $ 8,646 $ 8,999 $ 9,645
Contract assets, change (1,329) (999)    
Contract liabilities        
Contract liabilities - current 69,526 62,499 71,246 59,531
Contract liabilities - current, change (1,720) 2,968    
Contract liabilities - long-term 2,549 2,377 $ 2,189 $ 1,820
Contract liabilities - long-term, change $ 360 $ 557