Fair Value Disclosures - Assets and Liabilities Measured at Fair Value (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Interest Rate Swap
Assets:
Interest rate swaps	$ 0
Liabilities:
Interest rate swaps	(10,300,000)
Recurring | SERP
Assets:
SERP	2,433,000	$ 1,792,000
Recurring | Interest Rate Swap
Assets:
Interest rate swaps	0	5,549,000
Liabilities:
Interest rate swaps	(10,255,000)	(3,726,000)
Recurring | Level 1 | SERP
Assets:
SERP	0	0
Recurring | Level 1 | Interest Rate Swap
Assets:
Interest rate swaps	0	0
Liabilities:
Interest rate swaps	0	0
Recurring | Level 2 | SERP
Assets:
SERP	2,433,000	1,792,000
Recurring | Level 2 | Interest Rate Swap
Assets:
Interest rate swaps	0	5,549,000
Liabilities:
Interest rate swaps	(10,255,000)	(3,726,000)
Recurring | Level 3 | SERP
Assets:
SERP	0	0
Recurring | Level 3 | Interest Rate Swap
Assets:
Interest rate swaps	0	0
Liabilities:
Interest rate swaps	$ 0	$ 0