Common Stock and Other Equity Related Transactions Common Stock and Other Equity Related Transactions - Common Stock, OP Units, and Distributions (Details) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Units of Partnership Interest, Amount	7,207,678				7,231,967				7,667,723				7,207,678	7,231,967	7,667,723
Common Stock Outstanding [Roll Forward]
Shares outstanding at January 1,				83,879,779				83,313,677				83,193,310	83,879,779	83,313,677	83,193,310
Common stock issued through conversion of OP Units													24,289	435,756	29,566
Common stock issued through exercise of options													220,000	0	20,000
Stock Issued During Period, Shares, Restricted Stock Award, Gross													158,013	186,666	173,332
Common stock issued through ESPP and Dividend Reinvestment Plan													20,134	31,203	19,013
Common stock repurchased and retired													49,150	87,523	121,544
Shares outstanding at December 31,	84,253,065				83,879,779				83,313,677				84,253,065	83,879,779	83,313,677
Share Based Compensation Arrangement By Share Based Payment Award Repurchased Shares For Taxes													$ 66.20	$ 51.62	$ 36.48
Percentage Of Ownership Interests	92.10%				92.10%								92.10%	92.10%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	7.90%				7.90%								7.90%	7.90%
Disclosure Regular Quarterly Distributions Declared And Paid To Common Stockholders And Common O P Unit Non Controlling Interests [Abstract]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.375	$ 0.375	$ 0.375	$ 0.375	$ 0.325	$ 0.325	$ 0.325	$ 0.325	$ 0.25	$ 0.25	$ 0.25	$ 0.25
Dividends Payable, Date of Record	Dec. 28, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	Dec. 26, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 27, 2013	Sep. 27, 2013	Jun. 28, 2013	Mar. 28, 2013
Dividends Payable, Date to be Paid	Jan. 08, 2016	Oct. 09, 2015	Jul. 10, 2015	Apr. 10, 2015	Jan. 09, 2015	Oct. 10, 2014	Jul. 11, 2014	Apr. 11, 2014	Jan. 10, 2014	Oct. 11, 2013	Jul. 12, 2013	Apr. 12, 2013