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Debt Obligations, net (Schedule of Debt) (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2018 | Jun. 30, 2018 | Sep. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Oct. 31, 2017 | Aug. 31, 2016 | Jun. 30, 2016
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 3,928,372,000 |  | $ 3,928,372,000 |  | $ 3,928,372,000 |  | $ 3,539,991,000 |  |  |
Debt discounts and deferred financing costs, net |  | (58,796,000) |  | (58,796,000) |  | (58,796,000) |  | (63,591,000) |  |  |
Total debt obligations, net |  | 3,869,576,000 |  | 3,869,576,000 |  | 3,869,576,000 |  | 3,476,400,000 |  |  |
Interest costs capitalized |  |  |  | 2,100,000 | $ 2,000,000 | 4,500,000 | $ 4,000,000 |  |  |  |
2015 $325 million Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | 0 |  | 0 |  | $ 0 |  | 325,000,000 |  |  |
Converted term loan, term |  |  |  |  |  | 1 year |  |  |  |  |
2015 $325 million Revolving Credit Facility | Minimum | Interest Rate Category One |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.25% |  |  |  |  |
2015 $325 million Revolving Credit Facility | Minimum | Interest Rate Category Two |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 2.25% |  |  |  |  |
2015 $325 million Revolving Credit Facility | Maximum | Interest Rate Category One |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.75% |  |  |  |  |
2015 $325 million Revolving Credit Facility | Maximum | Interest Rate Category Two |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 2.75% |  |  |  |  |
2015 $325 million Revolving Credit Facility | London Interbank Offered Rate (LIBOR) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 2.50% |  |  |  |  |
2015 $325 million Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.00% |  |  |  |  |
2015 $325 million Revolving Credit Facility | Federal Funds Effective Swap Rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 0.50% |  |  |  |  |
2016 Senior Term Loan |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | 650,000,000 |  | 650,000,000 |  | $ 650,000,000 |  | 399,000,000 |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.00% |  |  |  |  |
Debt instrument, face amount |  | $ 650,000,000.0 | $ 400,000,000.0 | 650,000,000.0 |  | $ 650,000,000.0 |  |  |  | $ 500,000,000.0 | $ 450,000,000.0
2016 Senior Term Loan | London Interbank Offered Rate (LIBOR) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  | 2.75% | 3.00% |  |  | 2.75% |  |  |  |  |
2016 Senior Term Loan | London Interbank Offered Rate (LIBOR) | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  | 0.75% |  |  |  |  |  |  |  |
2016 Senior Term Loan | London Interbank Offered Rate (LIBOR) | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.75% |  |  |  |  |
2016 Senior Term Loan | Federal Funds Effective Swap Rate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 0.50% |  |  |  |  |
Mortgages collateralized by net lease assets |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 670,872,000 |  | $ 670,872,000 |  | $ 670,872,000 |  | 208,491,000 |  |  |
Weighted average interest rate (as a percent) |  | 4.60% |  | 4.60% |  | 4.60% |  |  |  |  |
Mortgages collateralized by net lease assets | Minimum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rates (as a percent) |  | 3.62% |  | 3.62% |  | 3.62% |  |  |  |  |
Mortgages collateralized by net lease assets | Maximum |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rates (as a percent) |  | 7.26% |  | 7.26% |  | 7.26% |  |  |  |  |
Total secured credit facilities and mortgages |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 1,320,872,000 |  | $ 1,320,872,000 |  | $ 1,320,872,000 |  | 932,491,000 |  |  |
5.00% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 770,000,000 |  | $ 770,000,000 |  | $ 770,000,000 |  | 770,000,000 |  |  |
Stated interest rates (as a percent) |  | 5.00% |  | 5.00% |  | 5.00% |  |  |  |  |
4.625% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 400,000,000 |  | $ 400,000,000 |  | $ 400,000,000 |  | 400,000,000 |  |  |
Stated interest rates (as a percent) |  | 4.625% | 4.625% | 4.625% |  | 4.625% |  |  |  |  |
Debt instrument, face amount |  |  | $ 400,000,000.0 |  |  |  |  |  |  |  |
6.50% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 275,000,000 |  | $ 275,000,000 |  | $ 275,000,000 |  | 275,000,000 |  |  |
Stated interest rates (as a percent) |  | 6.50% |  | 6.50% |  | 6.50% |  |  |  |  |
6.00% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 375,000,000 |  | $ 375,000,000 |  | $ 375,000,000 |  | 375,000,000 |  |  |
Stated interest rates (as a percent) |  | 6.00% |  | 6.00% |  | 6.00% |  |  |  |  |
5.25% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 400,000,000 |  | $ 400,000,000 |  | $ 400,000,000 |  | 400,000,000 |  |  |
Stated interest rates (as a percent) |  | 5.25% | 5.25% | 5.25% |  | 5.25% |  |  |  |  |
Debt instrument, face amount |  |  | $ 400,000,000.0 |  |  |  |  |  |  |  |
3.125% senior convertible notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 287,500,000 |  | $ 287,500,000 |  | $ 287,500,000 |  | 287,500,000 |  |  |
Total debt obligations, net |  | $ 259,600,000 |  | $ 259,600,000 |  | $ 259,600,000 |  |  |  |  |
Stated interest rates (as a percent) |  | 3.125% | 3.125% | 3.125% |  | 3.125% |  |  | 3.125% |  |
Convertible debt, conversion ratio (in shares per par value) |  |  |  |  |  | 64.36 |  |  |  |  |
Convertible debt, conversion price (in dollars per share) |  | $ 15.54 |  | $ 15.54 |  | $ 15.54 |  |  |  |  |
Liability component of convertible debt |  |  | $ 221,800,000 |  |  |  |  |  | $ 34,000,000 |  |
Carrying value of equity component of convertible debt |  |  | 22,500,000 |  |  |  |  |  | 3,400,000 |  |
Debt instrument, face amount |  |  | $ 250,000,000.0 |  |  |  |  |  | $ 37,500,000.0 |  |
Debt instrument, unamortized discount |  | $ 22,900,000 |  | $ 22,900,000 |  | $ 22,900,000 |  |  |  |  |
Interest expense, debt |  |  |  | 2,200,000 |  | 4,500,000 |  |  |  |  |
Amortization of debt discount |  |  |  | $ 1,200,000 |  | $ 2,300,000 |  |  |  |  |
Effective interest rate |  | 5.20% |  | 5.20% |  | 5.20% |  |  |  |  |
Unsecured Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | $ 2,507,500,000 |  | $ 2,507,500,000 |  | $ 2,507,500,000 |  | 2,507,500,000 |  |  |
Trust preferred securities |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations |  | 100,000,000 |  | 100,000,000 |  | $ 100,000,000 |  | $ 100,000,000 |  |  |
Basis point spread on variable interest rate (as a percent) |  |  |  |  |  | 1.50% |  |  |  |  |
Subsequent Event | 5.00% senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rates (as a percent) | 5.00% |  |  |  |  |  |  |  |  |  |
Redemption of senior debt | $ 273,000,000 |  |  |  |  |  |  |  |  |  |
Net lease venture |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt obligations, net |  | $ 464,700,000 |  | $ 464,700,000 |  | $ 464,700,000 |  |  |  |  |

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