Long-Term Debt (Narrative) (Details) (USD $)			3 Months Ended				3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Line of Credit [Member]	Mar. 31, 2014 Unsecured Debt [Member]	Mar. 31, 2014 Secured Debt [Member]	May 28, 2010 Secured Debt [Member]	Mar. 31, 2014 Maximum [Member] Line of Credit [Member]	Mar. 31, 2014 Minimum [Member] Line of Credit [Member]	Mar. 31, 2014 Period from current report date to November 30, 2015 Unsecured Debt [Member]	Mar. 31, 2014 Period from January 1, 2012 through November 7, 2012 Secured Debt [Member]
Credit Facility
Borrowing capacity of new revolving credit agreement			$ 475,000,000
Line of Credit Facility, Expiration Date			Jun. 01, 2018
Debt instruments interest rate base rate plus							1.00%	0.25%
Debt instruments interest rate Libor plus							2.00%	1.25%
Unused capacity commitment fee, percentage							0.40%	0.25%
Senior Unsecured Debt
Unsecured Debt	250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage				5.625%	8.04%					6.04%
Debt Instrument, Maturity Date				Nov. 30, 2020	May 28, 2020
Redeemable Principal Percentage				35.00%
Future Redemption Price of Debt During Eligibility Period, as a Percentage of Principal Amount									105.625%
Senior Secured Debt
Senior Secured Notes	$ 66,964,000	$ 69,643,000				$ 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