Commitments and Contingencies - Construction Activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft² property
Other Commitments [Line Items]
Number of Properties | property	199
Approximate Square Feet | ft²	14,800,000
Medical Office Building [Member]
Other Commitments [Line Items]
Construction in Progress Balance	$ 33,107
Total Funded During the Year	27,648
Total Amount Funded	33,407
Estimated Remaining Fundings (unaudited)	42,713
Estimated Total Investment (unaudited)	$ 76,120
Approximate Square Feet | ft²	189,000
North Carolina [Member] | Medical Office Building [Member]
Other Commitments [Line Items]
Number of Properties | property	1
Construction in Progress Balance	$ 9,586
Total Funded During the Year	6,099
Total Amount Funded	9,586
Estimated Remaining Fundings (unaudited)	2,414
Estimated Total Investment (unaudited)	$ 12,000
Approximate Square Feet | ft²	38,000
Washington [Member] | Medical Office Building [Member]
Other Commitments [Line Items]
Number of Properties | property	1
Construction in Progress Balance	$ 23,521
Total Funded During the Year	21,549
Total Amount Funded	23,821
Estimated Remaining Fundings (unaudited)	40,299
Estimated Total Investment (unaudited)	$ 64,120
Approximate Square Feet | ft²	151,000