Condensed Consolidated Statements of Stockholders' Equity - 3 months ended Mar. 31, 2016 - 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, 2015		118,903,312	1,120,067	118,903,000	1,120,000
Beginning balance at Dec. 31, 2015	$ 1,372,686			$ 1,189	$ 11	$ 469,152	$ (883)	$ 55,260	$ 524,729	$ 839,953	$ 8,004
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units and Class B shares to Class A shares (in shares)				1,723,000	(13,000)
Conversion of operating partnership units and Class B shares to Class A shares	0			$ 17	$ 0	6,858	(12)		6,863	(6,863)
Equity compensation:
LTIP units	2,000									2,000
Restricted stock, net of forfeitures (in shares)				14,000
Restricted stock, net of forfeitures	97					97			97
Dividends and distributions	(23,142)							(10,318)	(10,318)	(12,590)	(234)
Net income	16,705							7,428	7,428	9,043	234
Unrealized loss on valuation of interest rate swap agreements	(19,371)						(8,731)		(8,731)	(10,640)
Ending balance (in shares) at Mar. 31, 2016		120,639,410	1,107,290	120,640,000	1,107,000
Ending balance at Mar. 31, 2016	$ 1,348,975			$ 1,206	$ 11	$ 476,107	$ (9,626)	$ 52,370	$ 520,068	$ 820,903	$ 8,004