Summary of Significant Accounting Policies - Fair Value Measurements (Details) - Recurring basis - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 699,000	$ 448,000
Interest rate swaps	0	0
Fair value	699,000	448,000
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Interest rate swaps	(1,549,000)	(2,847,000)
Fair value	(1,549,000)	(2,847,000)
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Interest rate swaps	0	0
Fair value	$ 0	$ 0