Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2020
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	1,902
Common stock shares issued through dividend reinvestment plan	2,747	2,069	2,272
Number of shares of stock grants withheld	74,173	84,710	68,565
Common shares issued under Employee Stock Purchase Plan	20,161
Number of shares forfeited	7,683
Treasury Stock, Shares, Acquired	1,225,790
Treasury Stock Acquired, Average Cost Per Share	$ 149.99
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 316,148,000
Amended 2005 Stock Repurchase Program [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 500,000,000
2020 Stock Repurchase Program [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 500,000,000
Continuous Equity Program CEP V [Member]
Class of Stock [Line Items]
Issuance of common stock, net of withholdings (in shares)	0
Maximum value of shares of common stock that can be sold	$ 1,000,000,000
Common stock value, remaining to be authorized under continuous equity program	$ 752,878,000
Maximum [Member] | Continuous Equity Program CEP V [Member]
Class of Stock [Line Items]
Percentage of compensation received by sales agent	1.50%
Restricted Stock and Restricted Stock Converted From Performance Shares
Class of Stock [Line Items]
Common stock shares issued in connection with stock grants	165,545	152,502	187,010