Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 118,253	$ 107,250	$ 79,928
Other comprehensive loss:
Unrealized loss on valuation of interest rate swap agreements	(11,658)	(3,054)	(1,922)
Amount reclassified into interest expense	1,142	0	0
Other comprehensive loss	(10,516)	(3,054)	(1,922)
Comprehensive income	107,737	104,196	78,006
Net income attributable to non-controlling interests and private perpetual preferred unitholders	(55,606)	(55,794)	(46,198)
Other comprehensive loss attributable to non-controlling interests	4,901	1,576	1,100
Comprehensive income attributable to common stockholders	$ 57,032	$ 49,978	$ 32,908