Long-Term Debt (Narrative) (Details) (USD $)			12 Months Ended							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Line of Credit [Member]	Dec. 31, 2012 Unsecured Debt [Member]	Dec. 31, 2012 Secured Debt [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Dec. 31, 2012 Other Debt Obligations [Member]	Dec. 31, 2012 Maximum [Member] Line of Credit [Member]	Dec. 31, 2012 Maximum [Member] Unsecured Debt [Member]	Dec. 31, 2012 Minimum [Member] Line of Credit [Member]	Dec. 31, 2012 Period from current report date to November 30, 2015 Unsecured Debt [Member]	Dec. 31, 2012 Period from January 1, 2012 through November 7, 2012 Secured Debt [Member]
Long-term Debt, by Maturity [Abstract]
Repayments of Principal in Next Twelve Months	$ 17,407,000
Repayments of Principal after Year Five	283,627,000
Long-term Debt, Maturing in Years Two and Three [Abstract]
Repayments of Principal in Year Two	17,878,000
Repayments of Principal in Year Three	14,679,000
Long-term Debt, Maturing in Years Four and Five [Abstract]
Repayments of Principal in Year Four	12,585,000
Repayments of Principal in Year Five	291,936,000
Credit Facility
Borrowing capacity of new revolving credit agreement			475,000,000
Line of Credit Facility, Expiration Date			Jun. 01, 2017
Debt instruments interest rate base rate plus								1.25%		0.50%
Debt instruments interest rate Libor plus								2.25%		1.50%
Unused capacity commitment fee, percentage								0.40%		0.20%
Senior Unsecured Debt
Unsecured Debt	250,000,000	0
Debt Instrument, Interest Rate, Stated Percentage				5.625%	8.04%							6.04%
Debt Instrument, Maturity Date				Nov. 30, 2020	May 28, 2020	Dec. 31, 2026	Dec. 31, 2019
Redeemable Principal Percentage				35.00%
Future Redemption Price of Debt During Eligibility Period, as a Percentage of Principal Amount											105.625%
Liquidated Damages Percentage									1.00%
Senior Secured Debt
Senior Secured Notes	75,000,000	75,000,000
Debt Instrument, Interest Rate, Stated Percentage				5.625%	8.04%							6.04%
Debt Instrument, Maturity Date				Nov. 30, 2020	May 28, 2020	Dec. 31, 2026	Dec. 31, 2019
Debt Instrument, Interest Rate Increase					0.02
Other Long-term Debt [Abstract]
Book Value of Collateralized By Certain Assets							$ 89,595,000