Fair Value Measurements - Fair Value of Other Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair value disclosures
Long-term debt	$ 946,509	$ 1,133,924
Current maturities	0	(188,000)
Long-term debt, excluding current maturities	946,509	945,924
Carrying Amount
Fair value disclosures
Long-term debt	946,509	1,133,924
Current maturities	0	(188,000)
Long-term debt, excluding current maturities	946,509	945,924
Estimated Fair Value
Fair value disclosures
Long-term debt	1,010,687	1,213,811
Current maturities	0	(189,332)
Long-term debt, excluding current maturities	$ 1,010,687	$ 1,024,479

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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