Long-Term Debt and Loan Agreements - Additional Information (Details)		1 Months Ended	3 Months Ended		12 Months Ended
	May 30, 2014 USD ($)	Oct. 31, 2017 USD ($) NoteHolder	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2019 USD ($)	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Long-term Debt			$ 152,632,000		$ 78,000,000	$ 152,632,000
Loss on extinguishment of debt			(1,900,000)		0	1,888,000	$ 0
Unamortized deferred financing costs			1,596,000		1,210,000	1,596,000
Interest Expense [Member]
Debt Instrument [Line Items]
Amortization expense of deferred financing costs					386,000	508,000	$ 466,000
Minimum [Member]
Debt Instrument [Line Items]
Long-term Debt					$ 11,000,000
Interest rate					4.67%
Maximum [Member]
Debt Instrument [Line Items]
Long-term Debt					$ 40,000,000
Interest rate					5.45%
Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Face value of debt instrument with offer to be repurchased									$ 100,000,000
Debt instrument repurchase amount		$ 22,000,000
Outstanding principal balance of notes purchased		22,000,000
Debt instrument repurchase amount including make-whole premium		23,800,000
Debt instrument repurchase make-whole premium amount		$ 1,800,000
Debt instrument repurchase date		Oct. 31, 2017
Number of note holder accepted the offer | NoteHolder		1
Loss on extinguishment of debt			1,900,000
Unamortized deferred financing costs			$ 100,000			$ 100,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity on line of credit	$ 300,000,000			$ 200,000,000	$ 200,000,000
Loan maturity period	2018-12			2022-03
Remaining amount available under the line of credit					195,600,000
Letters of credit					$ 4,400,000
Interest rate during period					5.75%	4.94%	4.69%
Loan Agreement [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Letters of credit								$ 2,000,000