Equity (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	280,000,000		280,000,000
Preferred stock, shares authorized (in shares)	50,000,000		50,000,000
Common stock issued through the dividend reinvestment plan (in shares)	566	1,165
Number of shares of stock grants withheld (in shares)	67,609	57,172
Stock issued during period, shares, share-based compensation, forfeited (in shares)	1,829
Continuous Equity Program CEP IV
Class of Stock [Line Items]
Maximum value of shares of common stock that can be sold (in dollars)	$ 1,000,000,000
Common stock value, remaining to be authorized under continuous equity program	$ 892,915,000
Maximum | Continuous Equity Program CEP IV
Class of Stock [Line Items]
Percentage of compensation received by sales agent	2.00%
Restricted Stock and Restricted Stock Converted From Performance Shares
Class of Stock [Line Items]
Equity instruments granted (in shares)	182,998	198,502