Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Class A [Member]	Common Class B [Member]	Total Stockholders' Equity [Member]	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Noncontrolling Interest [Member]	Private Perpetual Preferred Units [Member]
Beginning balance at Dec. 31, 2013	$ 1,003,185			$ 385,158	$ 945	$ 11	$ 316,558	$ 67,644	$ 618,027
Beginning balance (in shares) at Dec. 31, 2013		94,484,023	1,122,130		94,484,000	1,122,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued		2,556,000	110,000
Common Stock, Value, Issued	379,328	25	1	44,398			44,372		334,930
Issuance of private perpetual preferred units in exchange for common units										(8,261)
Equity component of senior unsecured notes	13,204			4,857			4,857			8,347
Net income	59,246			22,525				22,525	36,480	241
Equity compensation:
LTIP units	2,480								2,480
Restricted stock, net of forfeitures					(5,000)
Restricted stock, net of forfeitures	428			428			428
Dividends and distributions	(64,768)			(24,601)				(24,601)	(39,926)	(241)
Ending balance at Sep. 30, 2014	$ 1,393,103			$ 432,765	$ 970	$ 12	$ 366,215	$ 65,568	$ 952,077	$ 8,261
Ending balance (in shares) at Sep. 30, 2014		97,035,359	1,232,123		97,035,000	1,232,000