Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 117,253	$ 118,253	$ 107,250
Other comprehensive loss:
Unrealized loss on valuation of interest rate swap agreements	(2,721)	(11,658)
Unrealized loss on valuation of interest rate swap agreements			(3,054)
Amount reclassified into interest expense	1,845	1,142
Amount reclassified into interest expense			0
Other comprehensive loss	(876)	(10,516)	(3,054)
Comprehensive income	116,377	107,737	104,196
Net income attributable to non-controlling interests and private perpetual preferred unitholders	(51,650)	(55,606)	(55,794)
Other comprehensive loss attributable to non-controlling interests	382	4,901	1,576
Comprehensive income attributable to common stockholders	$ 65,109	$ 57,032	$ 49,978