Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Disclosure of Cash Flow Information:
Interest paid	$ 64,988	$ 50,883	$ 52,688
Income taxes paid	1,333	1,059	996
Supplemental Disclosure of Noncash Investing and Financing Activities:
Accrued capital expenditures	3,155	5,092	5,696
Debt and interest rate swaps assumed and entered into in connection with an acquisition	286,000	28,163	0
Dividend distributions declared, but not paid	63,823	43,867	37,886
Issuance of operating partnership units in connection with acquisitions	1,125	71,754	0
Note receivable included in the consideration of a disposition	0	12,737	0
Note receivable retired in connection with an acquisition	8,611	0	0
Redeemable noncontrolling interest assumed in connection with an acquisition	0	4,773	0
Redemption of noncontrolling interest	$ 5,943	$ 5,709	$ 0