Hedging Activities - Balance Sheet Classification and Fair Values (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net			$ 2,148,000		$ 3,598,000
Interest Rate Cash Flow Hedge Liability At Fair Value	$ 2,789,000		2,789,000		4,672,000
Interest Expense [Member]
Derivative Instruments Gain Loss [Line Items]
Amount and location of expense reclassified from AOCI into expense (effective portion)	(672,000)	$ (640,000)	(1,974,000)	$ (1,105,000)
Other Noncurrent Liabilities [Member]
Derivative Instruments Gain Loss [Line Items]
Interest Rate Cash Flow Hedge Liability At Fair Value	$ 2,789,000		2,789,000		4,672,000
Interest Rate Swap [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net			$ 2,148,000		$ 3,598,000