Debt Interest Rate Risk Management (Details) (USD $)	3 Months Ended	12 Months Ended								12 Months Ended				12 Months Ended					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2012 Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2012 Interest Rate Swap [Member] Cash Flow Hedging, Added 2012 [Member]	Dec. 31, 2012 Previous Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2011 Previous Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2012 Other Liabilities [Member] Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2011 Other Liabilities [Member] Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member] Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss) [Member] Interest Rate Swap [Member] Cash Flow Hedging [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2011 Maximum [Member] Option (b) [Member]	Dec. 31, 2011 Maximum [Member] Option (a) [Member]	Dec. 31, 2011 Minimum [Member]	Dec. 31, 2011 Minimum [Member] Option (b) [Member]	Dec. 31, 2011 Minimum [Member] Option (a) [Member]	Jun. 30, 2012 Senior Notes [Member] 6.25% Interest Rate [Member]	Mar. 31, 2012 Senior Notes [Member] 6.25% Interest Rate [Member]
Debt Instrument [Line Items]
Proceeds from Hedge, Financing Activities					$ 1,900,000
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments		0	0		1,464,000
Line of credit facility, amount outstanding	421,000,000	421,000,000					305,000,000	155,000,000	150,000,000
Derivative, Cost of Hedge											6,000,000
Long-term debt, fixed interest rate							0.99%		0.74%
Debt instrument, basis spread on variable rate							2.25%		2.25%								2.75%	1.75%		1.75%	0.75%
Debt instrument, effective interest rate							3.24%		2.99%		6.24%
Accumulated other comprehensive loss	(4,279,000)	(4,279,000)	(6,464,000)	[1]			(4,300,000)
Unrecognized loss on cash flow hedges										(800,000)				3,430,000	520,000
Remainder of cash flow hedges to be transferred from AOCI to interest expense							3,400,000
Derivative liabilities, fair value												3,430,000	520,000
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	1,000,000
Line of Credit Facility, Commitment Fee Percentage																0.50%			0.30%
Stated interest rate, senior notes																						6.25%	6.25%
Cash Flow Hedge Loss Reclassified to Earnings		$ 0	$ 0	[1]	$ (1,076,000)	[1]

[1] (1) Restated as described in Note 2.