Derivative Financial Instruments - Derivative Gains (Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 01, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Document Fiscal Year Focus	2015
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 9,200
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(10,089)	$ (49,968)	$ 30,985
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(9,152)	(9,353)	(9,433)
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	0	0	0
Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	8,300
Partnership Interest [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss on settlement of derivative instruments	7,267	(4,648)	0
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ (10,089)	$ (49,968)	$ 30,985
3.90% unsecured maturing 11/1/2025 [Member] | Unsecured Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt Instrument, Face Amount				$ 250,000
Debt Instrument, Interest Rate, Stated Percentage				3.90%