Long Term Debt (Credit Facility and Mortgage Note) (Details) (USD $)	0 Months Ended			0 Months Ended
	Jan. 03, 2012	Dec. 31, 2012	Dec. 31, 2011	Jan. 03, 2013 After 1 Year of Meeting Supply Target [Member] Subsequent Event [Member]	Dec. 31, 2012 Revolving Line of Credit [Member]	Dec. 31, 2011 Revolving Line of Credit [Member]	Jan. 17, 2013 Revolving Line of Credit [Member] Amended and Restated Amount of Debt [Member] Subsequent Event [Member]	Dec. 31, 2012 Revolving Line of Credit [Member] Alternate Base Rate [Member]	Dec. 31, 2012 Revolving Line of Credit [Member] LIBOR Rate [Member]	Dec. 31, 2012 Letters of Credit [Member]	Dec. 31, 2012 Mortgages Notes [Member]	Dec. 31, 2011 Mortgages Notes [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 250,000,000		$ 350,000,000
Long-term debt outstanding		161,852,000	143,509,000		153,000,000	80,000,000					8,625,000	9,594,000
Line of credit facility, available borrowing capacity					87,200,000
Letters of credit outstanding										9,800,000
Basis spread on variable rate								1.00%	1.75%
Debt interest rate											8.25%
Interest rate at period end									2.22%
Up-front payment	63,000,000
Additional contingent cash payment	84,000,000
Conditional payment, amount paid				$ 34,000,000