Related Party Transactions and Arrangements - Schedule of Revenue (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 29, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Related-party revenues		$ 106,721	$ 118,418	$ 110,812
Affiliated Entity [Member] | Revolving Credit Facility [Member] | Credit Facility [Member]
Related Party Transaction [Line Items]
Interest income on Affiliate Lines of Credit		262	453	1,275
Offering-related fees and reimbursements [Member]
Related Party Transaction [Line Items]
Related-party revenues		16,096	36,526	24,412
Selling commissions [Member]
Related Party Transaction [Line Items]
Related-party revenues		7,746	19,943	14,101
Dealer manager and distribution fees [Member]
Related Party Transaction [Line Items]
Related-party revenues		5,021	8,300	5,133
Reimbursement revenue [Member]
Related Party Transaction [Line Items]
Related-party revenues		3,329	8,283	5,178
Transaction service fees and reimbursements [Member]
Related Party Transaction [Line Items]
Related-party revenues		13,929	12,533	25,880
Acquisition fees [Member]
Related Party Transaction [Line Items]
Related-party revenues		11,049	9,513	18,742
Financing coordination fee [Member]
Related Party Transaction [Line Items]
Related-party revenues		100	220	0
Disposition fee revenue [Member]
Related Party Transaction [Line Items]
Related-party revenues		0	0	4,974
Disposition fee revenue [Member] | Corporate Income Trust [Member]
Related Party Transaction [Line Items]
Related-party revenues	$ 4,400
Reimbursement revenues [Member]
Related Party Transaction [Line Items]
Related-party revenues		2,780	2,800	2,164
Management fees and reimbursements [Member]
Related Party Transaction [Line Items]
Related-party revenues		76,434	68,906	59,245
Asset and property management fees and leasing fees [Member]
Related Party Transaction [Line Items]
Related-party revenues		220	220	452
Advisory and performance fee revenue [Member]
Related Party Transaction [Line Items]
Related-party revenues		57,765	51,099	44,948
Reimbursement revenues [Member]
Related Party Transaction [Line Items]
Related-party revenues		$ 18,449	$ 17,587	$ 13,845
Selling commissions allowable [Member] | Cole REITs [Member]
Related Party Transaction [Line Items]
Selling commissions reallowed		100.00%	100.00%	100.00%
Dealer manager fees reimbursement [Member]
Related Party Transaction [Line Items]
Related-party revenues		$ 2,100	$ 3,200	$ 2,100
Revenue from managed real estate investment trusts, excluding fees from real estate programs [Member]
Related Party Transaction [Line Items]
Related-party revenues		$ 1,800	$ 1,400	$ 5,300