Supplemental Cash Flow Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	$ 13,705	$ 14,124
Cash paid for taxes	5,923	2,515
Supplemental Schedule of Non-Cash Activities
Distributions declared and unpaid	14,795	15,324	$ 303,131
Distributions reinvested	22,612	22,943
Shares tendered for redemption	10,986	12,394
Accrued capital additions	$ 13,881	$ 3,329