Credit Facility (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) item	Sep. 30, 2016	Dec. 31, 2016 USD ($)
Credit facility
Credit facility origination costs, net	$ 5,094		$ 7,303
Outstanding balance	$ 658,000		1,120,000
Credit Facility
Credit facility
Variable reference rate	LIBOR
Variable interest rate, basis points spread over variable reference rate (as a percent)	0.90%
Line of credit facility, commitment fee basis points (as a percent)	0.15%
Line of credit facility, all-in drawn variable interest rate (as a percent)	1.05%
Current borrowing capacity available	$ 1,340,000
Outstanding balance	$ 658,000		$ 1,120,000
Weighted average borrowing rate during the period (as a percent)	1.90%	1.40%
Weighted average interest rate at the end of the period (as a percent)	2.20%	1.40%
Credit Facility | Other assets, net
Credit facility
Credit facility origination costs, net	$ 5,100
Credit Facility | Unsecured debt
Credit facility
Maximum borrowing capacity	$ 2,000,000
Line Of Credit Facility, Number Of Extensions | item	2
Term of extension option	6 months
Increase in the maximum borrowing capacity after amendment	$ 1,000,000