Long-Term Debt and Loan Agreements - Additional Information (Details) - USD ($)		3 Months Ended			6 Months Ended
	May 30, 2014	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term Debt		$ 78,000,000			$ 78,000,000		$ 78,000,000
Long-term Debt		$ 76,983,000			$ 76,983,000		$ 76,790,000
Weighted average interest rate during period		6.27%	5.82%		6.25%	5.55%
Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 78,000,000			$ 78,000,000
Minimum [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 11,000,000			$ 11,000,000
Interest rate		4.67%			4.67%
Maximum [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 40,000,000			$ 40,000,000
Interest rate		5.45%			5.45%
Loan Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit	$ 300,000,000	$ 200,000,000		$ 200,000,000	$ 200,000,000
Loan maturity period	2018-12			2022-03
Remaining amount available under the line of credit		194,200,000			194,200,000
Letters of credit		$ 5,800,000			$ 5,800,000