Debt and Interest (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2014 Rate	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014 Rate	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012 Rate	Dec. 21, 2012
Debt Instrument [Line Items]
Term loan due 2017	$ 94,000,000			$ 94,000,000		$ 96,000,000
Revolver borrowings under the credit facility	45,000,000			45,000,000		67,000,000
Capital Lease Obligations	8,000			8,000		9,000
Debt and Capital Lease Obligations	139,008,000			139,008,000		163,009,000
Long-term Debt and Capital Lease Obligations, Current	4,004,000			4,004,000		4,002,000
Long-term Debt and Capital Lease Obligations	135,004,000			135,004,000		159,007,000
Line of Credit Facility, Current Borrowing Capacity								225,000,000
Repayments of Debt, Percent of Original Loan Balance								1.00%
Document Period End Date				Jun. 30, 2014
Line of Credit Facility, Remaining Borrowing Capacity	177,700,000			177,700,000
Debt, Weighted Average Interest Rate	2.40%			2.40%
Amortization of Financing Costs	131,000	141,000		263,000	288,000
Notional Amount of Interest Rate Derivatives							100,000,000
Debt Instrument, Interest Rate, Stated Percentage							0.9475%
Interest Rate Derivative Assets, at Fair Value	500,000			500,000
Interest Paid			2,394,000	2,160,000
Interest Expense [Abstract]
Interest expense	1,022,000	1,538,000		1,607,000	2,616,000
Deferred financing cost	131,000	141,000		263,000	288,000
Interest income	(9,000)	(10,000)		(14,000)	(21,000)
Less: amount capitalized for capital projects	(16,000)	(75,000)		(23,000)	(137,000)
Total interest expense, net	1,128,000	1,594,000		1,833,000	2,746,000
Letter of Credit, Sub-Facility [Member]
Debt Instrument [Line Items]
Revolver borrowings under the credit facility	2,300,000			2,300,000
Line of Credit Facility, Current Borrowing Capacity								20,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Term loan due 2017	$ 94,000,000			$ 94,000,000				$ 100,000,000