Fair Value Measures - Fair Value of Assets and Liabilities, Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Derivative assets	$ 351	$ 199
Liabilities:
Derivative liabilities	0	(3,547)
Fair Value, Measurements, Recurring [Member]
Assets:
CMBS	41,677	47,215
Derivative assets	351	199
Total assets	42,028	47,414
Liabilities:
Derivative liabilities		(3,547)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
CMBS	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities:
Derivative liabilities		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
CMBS	0	0
Derivative assets	351	199
Total assets	351	199
Liabilities:
Derivative liabilities		(3,547)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
CMBS	41,677	47,215
Derivative assets	0	0
Total assets	$ 41,677	47,215
Liabilities:
Derivative liabilities		$ 0