Fair Value Measurements - Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets [Abstract]
Note receivable	$ 0	$ 16,618
Liabilities:
Credit facility	(382,960)	(643,742)
Notes payable	(619,793)	(224,330)
Carrying amount | Recurring basis
Assets [Abstract]
Real estate loans receivable	78,944	39,154
Note receivable	0	16,618
Liabilities:
Credit facility	(389,000)	(651,000)
Notes payable	(625,000)	(225,000)
Mortgage debt	(169,850)	(123,632)
Carrying amount | Interest Rate Swap | Recurring basis
Assets [Abstract]
Derivative assets	12,760	13,881
Carrying amount | Embedded derivatives | Recurring basis
Liabilities:
Derivative liabilities	0	(5,571)
Fair value | Recurring basis
Assets [Abstract]
Real estate loans receivable	78,349	39,154
Note receivable	0	16,618
Liabilities:
Credit facility	(389,000)	(651,000)
Notes payable	(624,741)	(214,584)
Mortgage debt	(172,276)	(125,420)
Fair value | Interest Rate Swap | Recurring basis
Assets [Abstract]
Derivative assets	12,760	13,881
Fair value | Embedded derivatives | Recurring basis
Liabilities:
Derivative liabilities	$ 0	$ (5,571)