Condensed Consolidated Statements of Stockholders' Equity - 9 months ended Sep. 30, 2015 - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total Stockholders' Equity	Non-controlling Interests	Private Perpetual Preferred Units
Beginning balance (in shares) at Dec. 31, 2014		106,030,449	1,161,438	106,030,000	1,161,000
Beginning balance at Dec. 31, 2014	$ 1,381,097			$ 1,060	$ 12	$ 406,853	$ 0	$ 60,713	$ 468,638	$ 904,455	$ 8,004
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units and Class B shares to Class A shares (in shares)				10,773,000	(30,000)
Conversion of operating partnership units and Class B shares to Class A shares				$ 108	$ (1)	53,013			53,120	(53,120)
Equity compensation:
LTIP units, net of forfeitures	3,965									3,965
Restricted stock, net of forfeitures (in shares)				20,000
Restricted stock, net of forfeitures	294					294			294
Dividends and distributions	(68,920)							(29,056)	(29,056)	(39,162)	(702)
Net income	60,558							25,478	25,478	34,378	702
Unrealized loss on valuation of interest rate swap agreements	(4,384)						(1,903)		(1,903)	(2,481)
Ending balance (in shares) at Sep. 30, 2015		116,823,306	1,130,728	116,823,000	1,131,000
Ending balance at Sep. 30, 2015	$ 1,372,610			$ 1,168	$ 11	$ 460,160	$ (1,903)	$ 57,135	$ 516,571	$ 848,035	$ 8,004