Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 18,058	$ 19,145
Other comprehensive income:
Unrealized gain on valuation of interest rate swap agreements	4,180	1,394
Less amount reclassified into interest expense	599	0
Other comprehensive income	4,779	1,394
Comprehensive income	22,837	20,539
Net income attributable to non-controlling interests and private perpetual preferred unitholders	(8,290)	(9,160)
Other comprehensive income attributable to non-controlling interests	(2,160)	(658)
Comprehensive income attributable to common stockholders	$ 12,387	$ 10,721