Debt (Schedule Of Debt) (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Long-term Debt, By Type [Line Items]
Debt payable, net to 2038		$ 1,918,489	$ 1,872,942
Unsecured notes payable under credit facilities		180,000	149,500
Debt service guaranty liability		69,835	69,835
Obligations under capital leases		21,000	21,000
Total	[1]	$ 2,189,324	$ 2,113,277
Debt stated interest rate			3.50%	7.40%
Debt Payable To 2038 [Member] | Minimum [Member]
Schedule of Long-term Debt, By Type [Line Items]
Debt stated interest rate		1.73%	1.00%
Debt Payable To 2038 [Member] | Maximum [Member]
Schedule of Long-term Debt, By Type [Line Items]
Debt stated interest rate		8.57%	8.60%
Debt Payable To 2038 [Member] | Weighted Average [Member]
Schedule of Long-term Debt, By Type [Line Items]
Debt stated interest rate		4.30%	4.30%

[1] * Consolidated variable interest entities' assets and debt included in the above balances (see Note 15):