Investments - Schedule of Lease Intangible Assets and Liabilities, Net of Accumulated Amortization (Details) - USD ($) $ in Thousands |
Sep. 30, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Capital Leased Assets [Line Items] | ||
| Less: accumulated amortization | $ (261,322) | $ (243,320) |
| Intangible lease assets, net | 429,857 | 470,276 |
| Less: accumulated amortization | (59,459) | (53,688) |
| Intangible lease liabilities, net | 162,619 | 182,320 |
| In-place leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease assets, gross | 599,905 | 624,723 |
| Above-market leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease assets, gross | 91,274 | 88,873 |
| Below-market leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease liabilities, gross | $ 222,078 | $ 236,008 |