Common Shares (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands			3 Months Ended	6 Months Ended
	Apr. 12, 2022	Aug. 02, 2021	Mar. 31, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2020	Jul. 29, 2022	May 13, 2022	Dec. 31, 2021	Aug. 24, 2021
Number of common and preferred stock authorized to issue				185,000
Common shares, authorized				175,000					175,000
Preferred shares, authorized				10,000
Common Stock, Shares, Outstanding				106,500
Preferred Stock, Shares Outstanding				0
2.03% Unsecured credit facility [Member]
Maximum borrowing capacity under unsecured credit facility				$ 900,000
2021 ATM program
Maximum aggregate offering price of remaining common shares available for sale								$ 71,300
Maximum aggregate offering price of common shares		$ 500,000
Stock Issued During Period, Value, New Issues			$ 26,200
Stock Issued During Period, Shares, New Issues			200
AveragePricePerCommonShareSold			$ 165.01
2022 Equity offering
Stock Issued During Period, Value, New Issues	$ 490,300
Stock Issued During Period, Shares, New Issues	2,900
2022 ATM program
Maximum aggregate offering price of common shares				500,000
2022 ATM program | Subsequent Event [Member]
Maximum aggregate offering price of remaining common shares available for sale							$ 500,000
2020 ATM program
Maximum aggregate offering price of remaining common shares available for sale										$ 200
Maximum aggregate offering price of common shares						$ 362,700
Stock Issued During Period, Value, New Issues					$ 358,800
Stock Issued During Period, Shares, New Issues					2,900
AveragePricePerCommonShareSold					$ 126.64
April 2007 Repurchase Plan [Member]
Treasury stock allowed for repurchase				$ 500,000
April 2007 Repurchase Plan [Member] | Subsequent Event [Member]
Share Repurchase Program, Remaining Authorized Repurchase Amount							$ 269,500