Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized	280,000,000	280,000,000
Preferred stock, shares authorized	50,000,000	50,000,000
Common stock shares issued in connection with stock options exercised	40,534
Common stock shares issued through dividend reinvestment plan	2,272	3,058	2,396
Number of shares of stock grants withheld	68,565	60,319	53,453
Common shares issued under Employee Stock Purchase Plan	12,955
Number of shares forfeited	4,860
Issuance of common stock, net	$ 52,261,000	$ 111,093,000	$ 15,526,000
Continuous Equity Program CEP IV
Class of Stock [Line Items]
Issuance of common stock, net of withholdings (in shares)	244,924
Maximum value of shares of common stock that can be sold	$ 1,000,000,000
Percentage of compensation received by sales agent	2.00%
Shares issued, weighted average price per share (in dollars per share)	$ 189.14
Issuance of common stock, net	$ 45,629,000
Common stock value, remaining to be authorized under continuous equity program	$ 846,591,000
Maximum [Member] | 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]
Common stock shares issued in connection with stock grants	187,010	201,824	197,018