Debt (Schedule of Debt) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2014
Debt Instrument, Unamortized Discount	$ 6,204,000
Convertible senior notes - unsecured (net of discount of $5,862)	195,283,000	$ 194,138,000	$ 192,238,000
Revolving credit facility - unsecured	158,000,000	34,000,000
Unamortized Debt Issuance Expense	(9,740,000)	(11,814,000)
Debt, Long-term and Short-term, Combined Amount	1,115,981,000	914,443,000
Bank Term Loans [Member]
Bank term loans - unsecured	250,000,000	250,000,000
Private Placement [Member]
Bank term loans - unsecured	400,000,000	325,000,000
Debt Instrument, Name, HUD Mortgages [Member]
Fannie Mae term loans - secured (including discount of $1,573)	44,354,000	45,035,000
Debt Instrument, Name, Fannie Mae Term Loans [Member]
Fannie Mae term loans - secured (including discount of $1,573)	$ 78,084,000	$ 78,084,000