Derivative Instruments and Hedging Activities - Cash Flow Hedge Agreements (Details) - Interest Rate Swap - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivative [Line Items]
Amount of hedged item	$ 20,000
Amount of gain recognized in AOCI	1,281	$ 48	$ 651
Amount of gain reclassified from AOCI to interest expense	$ 92	$ 0	$ 0