Common Stock Common Stock (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Equity Distribution Agreement [Member]	Dec. 31, 2013 Equity Distribution Agreement [Member]	Jun. 30, 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
Common stock aggregate gross sales price, maximum						$ 100,000,000
Net proceeds from sale of stock	57,276,000	28,966,000	307,000	12,700,000	56,800,000
Sales commission and other fees				$ 129,000
Number of shares issued during the period under the Equity Distribution Agreement				278,914	1,381,494
Common stock average share price				$ 46.17	$ 41.61
Shares paid for tax withholding	34,552	22,789