Investments - Schedule of Activity in Real Estate Assets Held for Sale (Details)
$ in Thousands
6 Months Ended
Jun. 30, 2017
USD ($)
Property
Number of Properties  
Balance, December 31, 2016 | Property 44
Transfers from real estate investments held and used | Property 67
Sales | Property (49)
Transfers to real estate investments held and used | Property (7)
Balance, June 30, 2017 | Property 55
Carrying Value  
Balance, December 31, 2016 $ 160,570
Transfers from real estate investments held and used 157,839
Sales (112,101)
Transfers to real estate investments held and used (58,667)
Impairments (14,475)
Balance, June 30, 2017 $ 133,166