Common Stock Common Stock (Details) (USD $)	12 Months Ended			3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Equity Distribution Agreement [Member]	Jun. 30, 2012 Equity Distribution Agreement [Member]	Dec. 31, 2012 Equity Distribution Agreement [Member]
Class of Stock [Line Items]
Combined common and preferred stock, shares authorized	250,000,000	250,000,000
Common stock, shares authorized	200,000,000	200,000,000
Common stock, par or stated value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, par or stated value per share	$ 0.01	$ 0.01
Common stock reserved for incentive plan awards	2,265,957
CommonStockAggregateGrossSalesPriceMaximum					$ 100,000,000
Net proceeds from sale of stock	$ 28,966,000	$ 307,000	$ 235,000			$ 28,500,000
Number of shares issued during the period under the Equity Distribution Agreement				0		815,416
Shares paid for tax withholding	22,789	2,750