Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value of Financial Assets and Liabilities
Risk premium (as a percent)	1.83%
Cost
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities, net	$ 786,087	$ 786,227
Fair Value
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities, net	860,403	944,447
Fair Value | Level 1
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities, net	0	0
Fair Value | Level 2
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities, net	860,403	944,447
Fair Value | Level 3
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities, net	$ 0	$ 0