Financial Instruments - Credit Losses (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Expected loss rate		42.00%
Due from Employees	$ 44,723,000	$ 44,723,000	$ 43,670,000
2020	404,000	404,000
2019	476,000	476,000
2018	181,000	181,000
2017	748,000	748,000
2016	651,000	651,000
2015 and prior	3,157,000	3,157,000
Total	5,617,000	5,617,000
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,903,000	3,673,000
Additions and other adjustments	287,000	517,000
Ending balance	4,190,000	$ 4,190,000
Minimum [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Service Period		3 years
Maximum [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Service Period		10 years
Notes Receivable, Five Years and Older [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Ending balance	3,200,000	$ 3,200,000
Notes Receivable, Under Five Years [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Ending balance	$ 1,000,000.0	$ 1,000,000.0