Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Revolving credit facility - unsecured	$ 298,000	$ 300,000
Bank term loans - unsecured		400,000
Convertible senior notes - unsecured (net of discount of $5,862)	60,000	59,697
Unamortized Debt Issuance Expense	4,069	7,076
Debt, Long-term and Short-term, Combined Amount	1,499,285	1,440,465
Bank Term Loans [Member]
Bank term loans - unsecured	650,000	550,000
Private Placement [Member]
Bank term loans - unsecured	400,000	400,000
Debt Instrument, Name, HUD Mortgages [Member]
Fannie Mae term loans - secured (including discount of $1,573)	0	42,138
Debt Instrument, Unamortized Discount	(1,172)
Debt Instrument, Name, Fannie Mae Term Loans [Member]
Fannie Mae term loans - secured (including discount of $1,573)	95,354	95,706
Debt Instrument, Name, Convertible Senior Notes [Member]
Debt Instrument, Unamortized Discount	0	(303)
Debt Instrument, Name, Q3 2014 HUD Mortgages [Member]
Debt Instrument, Unamortized Discount	$ 0	$ (1,238)

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Amount, after accumulated amortization, of debt discount.

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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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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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