Fair Value Measurements - Fair Value of Other Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair value disclosures
Long-term debt	$ 1,219,790	$ 1,226,104
Current maturities	(87,000)	0
Long-term debt, excluding current maturities	1,132,790	1,226,104
Carrying Amount
Fair value disclosures
Long-term debt	1,219,790	1,226,104
Current maturities	(87,000)	0
Long-term debt, excluding current maturities	1,132,790	1,226,104
Estimated Fair Value
Fair value disclosures
Long-term debt	1,258,674	1,202,994
Current maturities	(89,210)	0
Long-term debt, excluding current maturities	$ 1,169,464	$ 1,202,994

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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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