Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 29,230	$ 35,489	$ 77,472	$ 85,993
Other comprehensive income (loss):
Unrealized gain (loss) on valuation of interest rate swap agreements	3,884	(1,638)	9,827	(14,654)
Less: amount reclassified into interest expense	427	359	1,562	402
Other comprehensive income (loss)	4,311	(1,279)	11,389	(14,252)
Comprehensive income (loss)	33,541	34,210	88,861	71,741
Net income attributable to non-controlling interests and private perpetual preferred unitholders	(12,888)	(16,683)	(34,711)	(40,618)
Other comprehensive (income) loss attributable to non-controlling interests	(1,881)	586	(5,045)	6,670
Comprehensive income (loss) attributable to common stockholders	$ 18,772	$ 18,113	$ 49,105	$ 37,793