Fair Value Measurements - Fair Value of Other Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair value disclosures
Long-term debt	$ 1,046,123	$ 1,133,924
Current maturities	(100,000)	(188,000)
Long-term debt, excluding current maturities	946,123	945,924
Carrying Amount
Fair value disclosures
Long-term debt	1,046,123	1,133,924
Current maturities	(100,000)	(188,000)
Long-term debt, excluding current maturities	946,123	945,924
Estimated Fair Value
Fair value disclosures
Long-term debt	1,121,176	1,213,811
Current maturities	(100,900)	(189,332)
Long-term debt, excluding current maturities	$ 1,020,276	$ 1,024,479