Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Class A [Member]	Common Class B [Member]	Total Stockholders' Equity [Member] USD ($)	Common Stock [Member] Common Class A [Member] USD ($)	Common Stock [Member] Common Class B [Member] USD ($)	Additional Paid-in Capital [Member] USD ($)	Retained Earnings [Member] USD ($)	Noncontrolling Interest [Member] USD ($)	Private Perpetual Preferred Units [Member] USD ($)
Beginning balance at Dec. 31, 2014	$ 1,381,097			$ 468,638	$ 1,060	$ 12	$ 406,853	$ 60,713	$ 904,455	$ 8,004
Beginning balance (in shares) at Dec. 31, 2014		106,030,449	1,161,438		106,030,000	1,161,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units and Class B shares to Class A shares (in shares)					4,543,000	(12,000)
Conversion of operating partnership units and Class B shares to Class A shares				19,538	46	(1)	19,493		(19,538)
Net income	7,888			3,138				3,138	4,516	234
Equity compensation:
LTIP units	1,559								1,559
Restricted stock, net of forfeitures (in shares)					25,000
Restricted stock, net of forfeitures	135			135			135
Dividends and distributions	(22,973)			(9,406)				(9,406)	(13,333)	(234)
Ending balance at Mar. 31, 2015	$ 1,367,706			$ 482,043	$ 1,106	$ 11	$ 426,481	$ 54,445	$ 877,659	$ 8,004
Ending balance (in shares) at Mar. 31, 2015		110,598,327	1,149,014		110,598,000	1,149,000