Equity (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
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 shares issued in connection with stock options exercised (in shares)	7,266
Common stock issued through the dividend reinvestment plan (in shares)	1,165	576
Number of shares of stock grants withheld (in shares)	57,172	48,189
Stock Issued During Period, Shares, Share-based Compensation, Forfeited (in shares)	236
Issuance of common stock, net	$ 56,817,000	$ 1,102,000
Continuous Equity Program CEP IV [Member]
Class of Stock [Line Items]
Common stock shares issued	306,177
Maximum value of shares of common stock that can be sold (in dollars)	$ 1,000,000,000
Shares issued, price per share (in dollars per share)	$ 186.44
Issuance of common stock, net	$ 56,228,000
Common stock value, remaining to be authorized under continuous equity program	$ 942,915,000
Maximum [Member] | Continuous Equity Program CEP IV [Member]
Class of Stock [Line Items]
Percentage of compensation received by sales agent	2.00%
Restricted Stock and Restricted Stock Converted From Performance Shares [Member]
Class of Stock [Line Items]
Restricted stock granted (in shares)	198,502	193,171