Condensed Consolidated Statements of Stockholders' Equity - 6 months ended Jun. 30, 2015 - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-in Capital	Retained Earnings	Total Stockholders' Equity	Noncontrolling Interest	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	$ 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)				7,067,000	(27,000)
Conversion of operating partnership units and Class B shares to Class A shares				$ 71	$ (1)	28,586		28,656	(28,656)
Net income	34,473						14,258	14,258	19,747	468
Equity compensation:
LTIP units, net of forfeitures	2,731								2,731
Restricted stock, net of forfeitures (in shares)				23,000
Restricted stock, net of forfeitures	193					193		193
Dividends and distributions	(45,948)						(19,068)	(19,068)	(26,412)	(468)
Ending balance (in shares) at Jun. 30, 2015		113,119,634	1,134,252	113,120,000	1,134,000
Ending balance at Jun. 30, 2015	$ 1,372,546			$ 1,131	$ 11	$ 435,632	$ 55,903	$ 492,677	$ 871,865	$ 8,004