Debt and Interest (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Rate	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Rate	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($) Rate	Dec. 21, 2012 USD ($)
Debt Instrument [Line Items]
Term loan due 2017	$ 90,000		$ 90,000		$ 92,000
Revolver borrowings under the credit facility	154,000		154,000		44,000
Capital Lease Obligations	3		3		5
Debt and Capital Lease Obligations	244,003		244,003		136,005
Long-term Debt and Capital Lease Obligations, Current	4,003		4,003		4,003
Long-term Debt and Capital Lease Obligations	240,000		$ 240,000		$ 132,002
Line of Credit Facility, Current Borrowing Capacity							$ 225,000
Repayments of Debt, Percent of Original Loan Balance							1.00%
Document Period End Date			Jun. 30, 2015
Line of Credit Facility, Remaining Borrowing Capacity	$ 70,100		$ 70,100
Debt, Weighted Average Interest Rate | Rate	2.20%		2.20%
Amortization of Financing Costs	$ 142	$ 131	$ 285	$ 263
Notional Amount of Interest Rate Derivatives						$ 100,000
Debt Instrument, Interest Rate, Stated Percentage | Rate						0.9475%
Interest Rate Derivative Assets, at Fair Value	100		100
Interest Paid			2,326	2,160
Interest Expense [Abstract]
Interest expense	1,306	1,022	2,332	1,607
Deferred financing cost	142	131	285	263
Interest income	(30)	(9)	(37)	(14)
Less: amount capitalized for capital projects	(15)	(16)	(26)	(23)
Total interest expense, net	$ 1,403	$ 1,128	$ 2,554	$ 1,833
Actual Total Leverage Ratio, Debt Covenant	1.89		1.89		0.98
Letter of Credit, Sub-Facility [Member]
Debt Instrument [Line Items]
Revolver borrowings under the credit facility	$ 900		$ 900
Line of Credit Facility, Current Borrowing Capacity							$ 20,000
Term Loan [Member]
Debt Instrument [Line Items]
Term loan due 2017	$ 90,000		$ 90,000				$ 100,000
High Range Ratio [Member]
Interest Expense [Abstract]
Debt Instrument, Covenant, Total Leverage Ratio							3.00
Debt Instrument, Covenant, Senior Leverage Ratio							2.50
Debt Instrument, Covenant, Fixed Charge Coverage Ratio							1.25
Low Range Ratio [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity							$ 25,000
Interest Expense [Abstract]
Debt Instrument, Covenant, Total Leverage Ratio							1.00
Debt Instrument, Covenant, Senior Leverage Ratio							1.00
Debt Instrument, Covenant, Fixed Charge Coverage Ratio							1.00
Senior Leverage Ratio Incurrence test [Member]
Interest Expense [Abstract]
Debt Instrument, Covenant, Senior Leverage Ratio							0.50
Senior Leverage Ratio Incurrence test [Member] | High Range Ratio [Member]
Interest Expense [Abstract]
Debt Instrument, Covenant, Senior Leverage Ratio							2.00
Senior Leverage Ratio Incurrence test [Member] | Low Range Ratio [Member]
Interest Expense [Abstract]
Debt Instrument, Covenant, Senior Leverage Ratio							1.00