Assets and Liabilities Measured at Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial assets (liabilities), Carrying value
Current and long-term debt, carrying amount	$ (2,988,067)	$ (2,803,381)
Financial assets (liabilities), Fair value
Current and long-term debt, fair value	$ (2,948,171)	$ (3,074,929)