Equity (Details 2) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 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
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	2,263
Common stock issued through the dividend reinvestment plan (in shares)	1,135	1,828
Number of shares of stock grants withheld (in shares)	67,854	59,019
Stock Issued During Period, Shares, Employee Stock Purchase Plans	6,613
Stock issued during period, shares, share-based compensation, forfeited (in shares)	4,434
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)	186,382	201,314