Debt (Summary Of The Balances Outstanding And Interest Rate Spread) (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Outstanding Balance, Line of credit
$250 Million Unsecured Term Loan ("First Term Loan") [Member]
Outstanding Balance, term loans	225,000	210,520
$300 Million Senior Unsecured Term Loan Agreement ("Second Term Loan")[Member]
Outstanding Balance, term loans	300,000	300,000
$200 Million Senior Unsecured Term Loan Agreement ("Third Term Loan")[Member]
Outstanding Balance, term loans	$ 200,000	$ 156,100
Minimum [Member] \| $250 Million Senior Unsecured Revolving Line Of Credit ("Line of Credit") [Member]
Basis spread on variable rate (in hundredths)	1.50%
Minimum [Member] \| $250 Million Unsecured Term Loan ("First Term Loan") [Member]
Basis spread on variable rate (in hundredths)	1.45%
Minimum [Member] \| $300 Million Senior Unsecured Term Loan Agreement ("Second Term Loan")[Member]
Basis spread on variable rate (in hundredths)	1.50%
Minimum [Member] \| $200 Million Senior Unsecured Term Loan Agreement ("Third Term Loan")[Member]
Basis spread on variable rate (in hundredths)	1.45%
Maximum [Member] \| $250 Million Senior Unsecured Revolving Line Of Credit ("Line of Credit") [Member]
Basis spread on variable rate (in hundredths)	2.25%
Maximum [Member] \| $250 Million Unsecured Term Loan ("First Term Loan") [Member]
Basis spread on variable rate (in hundredths)	2.20%
Maximum [Member] \| $300 Million Senior Unsecured Term Loan Agreement ("Second Term Loan")[Member]
Basis spread on variable rate (in hundredths)	2.25%
Maximum [Member] \| $200 Million Senior Unsecured Term Loan Agreement ("Third Term Loan")[Member]
Basis spread on variable rate (in hundredths)	2.20%

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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