Debt - Line of Credit (Details) (USD $)	12 Months Ended					12 Months Ended								0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Credit Agreement [Member]	Dec. 31, 2012 Credit Agreement [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Credit Agreement [Member] Minimum [Member]	Dec. 31, 2012 Credit Agreement [Member] Maximum [Member]	Dec. 31, 2012 Credit Agreement [Member] Adjusted Base Rate Advances [Member] Adjusted Base Rate [Member] Federal Funds Rate [Member] Minimum [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Credit Agreement [Member] Adjusted Base Rate Advances [Member] Adjusted Base Rate [Member] Eurodollar Rate [Member] Minimum [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Credit Agreement [Member] Adjusted Base Rate Advances [Member] Applicable Margin [Member] Minimum [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Credit Agreement [Member] Adjusted Base Rate Advances [Member] Applicable Margin [Member] Maximum [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Credit Agreement [Member] Eurodollar Advances [Member] Applicable Margin [Member] Minimum [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Letter of Credit [Member] Eurodollar Advances [Member] Applicable Margin [Member] Maximum [Member] Refinancing of Debt [Member]	Jan. 06, 2012 Credit Agreement 2012 [Member] Refinancing of Debt [Member]	Dec. 31, 2012 Line of Credit [Member] Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Contractual Term														5 years
Line of Credit Facility, Maximum Borrowing Capacity				$ 300,000,000
Line of Credit Facility, Commitment Fee Percentage						0.175%	0.35%
Line of Credit Facility, Amount Outstanding	94,000,000	120,000,000
Line of Credit Facility, Remaining Borrowing Capacity				206,000,000
Line of Credit, Weighted Average Interest Rate															1.60%
Line of Credit Facility, Available Additional Borrowing Capacity					200,000,000
Line of Credit, Description Of Variable Rate Basis				LIBOR
Line of Credit Facility, Basis Spread on Variable Rate								0.50%	1.00%	0.125%	0.75%	1.125%	1.75%
Interest Paid	4,300,000	1,100,000	7,200,000
Payments for Hedge, Financing Activities			$ 2,900,000