Common Stock and Other Equity Related Transactions - Common Stock, OP Units, and Distributions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Units of partnership interest (in shares)	5,834,100	7,170,000	7,207,678
Common Stock Outstanding [Roll Forward]
Shares outstanding at January 1, (shares)	85,529,386	84,253,065	83,879,779
Common stock issued through the At-The-Market Offering Program (in shares)	1,380,017	683,548	0
Common stock issued through conversion of OP Units (in shares)	1,335,900	37,678	24,289
Common stock issued through exercise of options (in shares)	220,000	440,000	220,000
Common stock issued through stock grants	130,426	133,717	158,014
Common stock forfeitures	(990)	0	0
Common stock issued through ESPP and Dividend Reinvestment Plan (in shares)	25,101	17,373	20,133
Common stock repurchased and retired (in shares)	(34,680)	(35,995)	(49,150)
Shares outstanding at December 31, (shares)	88,585,160	85,529,386	84,253,065
Share based payment award repurchased shares for taxes (usd per share)	$ 89.02	$ 72.22	$ 66.20
Percentage of ownership interests (in percentage)	93.80%	92.30%
Ownership percentage by noncontrolling owners (in percentage)	6.20%	7.70%