Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]	Stockholders' Equity [Member]	Non-Controlling Interests [Member]
Balance at Dec. 31, 2014	$ 1,500,886	$ 583	$ 2,027,404	$ (15,024)	$ (547,592)	$ 1,465,371	$ 35,515
Shares of class A common stock issued, net	1,029,540	354	1,029,186			1,029,540
Restricted class A common stock earned	12,960		12,960			12,960
Dividends reinvested	16		275		(259)	16
Deferred directors' compensation	375		375			375
Other comprehensive income (loss)	(17,734)			(17,734)		(17,734)
Net income	211,885				196,829	196,829	15,056
Dividends declared on common stock	(194,769)				(194,769)	(194,769)
Distributions to non-controlling interests	(37,428)						(37,428)
Balance at Dec. 31, 2015	2,505,731	937	3,070,200	(32,758)	(545,791)	2,492,588	13,143
Shares of class A common stock issued, net	8	8				8
Restricted class A common stock earned	19,045		19,045			19,045
Dividends reinvested	27		377		(350)	27
Deferred directors' compensation	375		375			375
Other comprehensive income (loss)	(23,444)			(23,444)		(23,444)
Net income	246,440				238,297	238,297	8,143
Dividends declared on common stock	(233,293)				(233,293)	(233,293)
Distributions to non-controlling interests	(21,286)						(21,286)
Balance at Dec. 31, 2016	2,493,603	945	3,089,997	(56,202)	(541,137)	2,493,603
Shares of class A common stock issued, net	391,568	134	391,434			391,568
Restricted class A common stock earned	23,584		23,584			23,584
Issuance of convertible notes	964		964			964
Dividends reinvested	44		444		(400)	44
Deferred directors' compensation	438		438			438
Other comprehensive income (loss)	26,496			26,496		26,496
Net income	217,968				217,631	217,631	337
Dividends declared on common stock	(243,262)				(243,262)	(243,262)
Contributions from non-controlling interests	12,165						12,165
Distributions to non-controlling interests	(6,162)						(6,162)
Balance at Dec. 31, 2017	$ 2,917,406	$ 1,079	$ 3,506,861	$ (29,706)	$ (567,168)	$ 2,911,066	$ 6,340