Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Feb. 01, 2018
Deferred Revenue Arrangement [Line Items]
Total return on stockholders' capital, exceeding benchmark	6.00%
Service agreement, cost of services	$ (3,200)
Other income, net	$ 7,436	$ 659
Cole Capital [Member] | Held-for-sale of Disposed of by Sale [Member]
Deferred Revenue Arrangement [Line Items]
Contingent consideration, payment period	6 years
Contingent consideration, maximum consideration receivable			$ 80,000
Service Agreement [Member]
Deferred Revenue Arrangement [Line Items]
Other income, net	$ 3,200