Revolving Credit Facilities and Mortgage Payable - Primary Credit Facility (Details) - Primary Credit Facility - Line of Credit - USD ($)	1 Months Ended	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2019
LIBOR based interest rates
Notes Payable and Long-Term Debt
Interest rate, effective percentage		2.89%
Alternate Base Rate based interest rates
Notes Payable and Long-Term Debt
Interest rate, effective percentage		4.88%
Revolving Credit Facility
Notes Payable and Long-Term Debt
Term of agreement (in years)	5 years
Maximum borrowing capacity	$ 400,000,000
Proceeds from lines of credit		$ 50,000,000
Repayments of lines of credit		50,000,000
Long-term line of credit		0
Outstanding letters of credit		549,000
Amount available under the credit agreement		$ 399,451,000
Maximum
Notes Payable and Long-Term Debt
Capacity available for letters of credit	$ 25,000,000