Long-Term Debt and Loan Agreements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	May 30, 2014	Dec. 13, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Letters of credit	$ 4,500,000		$ 4,500,000
Long-term debt, excluding unamortized deferred financing costs	197,930,000		197,930,000		$ 191,881,000
Less unamortized deferred financing fees	1,280,000		1,280,000		$ 1,631,000
Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit						$ 300,000,000	$ 200,000,000	$ 180,000,000
Remaining amount available under the line of credit	$ 196,300,000		$ 196,300,000
Interest rate during period	4.65%	4.74%	4.61%	4.63%