Debt Obligations, net (Schedule of Debt) (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2012	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Aug. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total debt obligations		$ 3,780,669,000		$ 3,780,669,000					$ 4,150,389,000
Debt discounts and deferred financing costs, net		(30,796,000)		(30,796,000)					(31,566,000)
Total debt obligations, net		3,749,873,000		3,749,873,000					4,118,823,000
Interest costs capitalized		1,400,000	$ 1,300,000	4,200,000	$ 4,000,000
2015 $250 Million Secured Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, face amount		250,000,000		250,000,000
Total debt obligations		0		$ 0					250,000,000
Converted term loan, term				1 year
2015 $250 Million Secured Revolving Credit Facility | Minimum | Interest Rate Category One
Debt Instrument [Line Items]
Debt instrument, margin				1.25%
2015 $250 Million Secured Revolving Credit Facility | Minimum | Interest Rate Category Two
Debt Instrument [Line Items]
Debt instrument, margin				2.25%
2015 $250 Million Secured Revolving Credit Facility | Maximum | Interest Rate Category One
Debt Instrument [Line Items]
Debt instrument, margin				1.75%
2015 $250 Million Secured Revolving Credit Facility | Maximum | Interest Rate Category Two
Debt Instrument [Line Items]
Debt instrument, margin				2.75%
2015 $250 Million Secured Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate, spread				2.75%
2015 $250 Million Secured Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate, spread				1.00%
2015 $250 Million Secured Revolving Credit Facility | Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Variable interest rate, spread				0.50%
2016 Senior Secured Credit Facility
Debt Instrument [Line Items]
Debt instrument, face amount						$ 500,000,000.0	$ 450,000,000.0
Total debt obligations		499,976,000		$ 499,976,000					0
Variable interest rate, spread				1.00%
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate, spread				4.50%
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate, spread				1.00%
2016 Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate, spread				3.50%
2016 Senior Secured Credit Facility | Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Variable interest rate, spread				0.50%
Mortgages collateralized by net lease assets
Debt Instrument [Line Items]
Total debt obligations		$ 232,721,000		$ 232,721,000					239,547,000
Stated interest rate, minimum				4.85%
Stated interest rate, maximum				7.26%
Weighted average interest rate		5.20%		5.20%
Mortgages collateralized by net lease assets | London Interbank Offered Rate (LIBOR) | Property One
Debt Instrument [Line Items]
Variable interest rate, spread				2.00%
2012 Secured Tranche A-2 Facility
Debt Instrument [Line Items]
Debt instrument, face amount	$ 470,000,000
Total debt obligations		$ 0		$ 0					339,717,000
Variable interest rate, spread	5.75%
2012 Secured Tranche A-2 Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate, spread				5.75%
2012 Secured Tranche A-2 Facility | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate, spread	1.25%
Total secured credit facilities and mortgages
Debt Instrument [Line Items]
Total debt obligations		732,697,000		$ 732,697,000					829,264,000
5.875% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 0		$ 0					261,403,000
Stated Interest Rates		5.875%		5.875%				5.875%
3.875% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 0		$ 0					265,000,000
Stated Interest Rates		3.875%		3.875%
3.00% senior convertible notes
Debt Instrument [Line Items]
Total debt obligations		$ 200,000,000		$ 200,000,000					200,000,000
Stated Interest Rates		3.00%		3.00%
Convertible debt conversion ratio				0.085
Convertible debt conversion price (usd per share)		$ 11.77		$ 11.77
1.50% senior convertible notes
Debt Instrument [Line Items]
Total debt obligations		$ 178,250,000		$ 178,250,000					200,000,000
Stated Interest Rates		1.50%		1.50%
Convertible debt conversion ratio				0.0578
Convertible debt conversion price (usd per share)		$ 17.29		$ 17.29
5.85% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 99,722,000		$ 99,722,000					99,722,000
Stated Interest Rates		5.85%		5.85%
9.00% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 275,000,000		$ 275,000,000					275,000,000
Stated Interest Rates		9.00%		9.00%
4.00% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 550,000,000		$ 550,000,000					550,000,000
Stated Interest Rates		4.00%		4.00%
7.125% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 300,000,000		$ 300,000,000					300,000,000
Stated Interest Rates		7.125%		7.125%
4.875% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 300,000,000		$ 300,000,000					300,000,000
Stated Interest Rates		4.875%		4.875%
5.00% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 770,000,000		$ 770,000,000					770,000,000
Stated Interest Rates		5.00%		5.00%
6.50% senior notes
Debt Instrument [Line Items]
Total debt obligations		$ 275,000,000		$ 275,000,000					0
Stated Interest Rates		6.50%		6.50%				6.50%
Unsecured Notes
Debt Instrument [Line Items]
Total debt obligations		$ 2,947,972,000		$ 2,947,972,000					3,221,125,000
Trust preferred securities
Debt Instrument [Line Items]
Total debt obligations		$ 100,000,000		$ 100,000,000					$ 100,000,000
Variable interest rate, spread				1.50%