Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Stockholders' Equity [Member]	Non-Controlling Interests [Member]	Class A Common Stock [Member] Common Stock [Member]
Balance at Dec. 31, 2014	$ 1,500,886	$ 2,027,404	$ (15,024)	$ (547,592)	$ 1,465,371	$ 35,515	$ 583
Shares of class A common stock issued, net	2				2		2
Restricted class A common stock earned	3,202	3,202			3,202
Dividends reinvested	3	60		(57)	3
Deferred directors' compensation	94	94			94
Other comprehensive loss	(16,732)		(16,732)		(16,732)
Net income	46,093			35,393	35,393	10,700
Dividends declared on common stock	(30,398)			(30,398)	(30,398)
Distributions to non-controlling interests	(452)					(452)
Balance at Mar. 31, 2015	1,502,698	2,030,760	(31,756)	(542,654)	1,456,935	45,763	585
Balance at Dec. 31, 2015	2,505,731	3,070,200	(32,758)	(545,791)	2,492,588	13,143	937
Shares of class A common stock issued, net	2				2		2
Restricted class A common stock earned	4,593	4,593			4,593
Dividends reinvested	6	88		(82)	6
Deferred directors' compensation	94	94			94
Other comprehensive loss	(687)		(687)		(687)
Net income	57,199			57,047	57,047	152
Dividends declared on common stock	(58,226)			(58,226)	(58,226)
Distributions to non-controlling interests	(6,879)					(6,879)
Balance at Mar. 31, 2016	$ 2,501,833	$ 3,074,975	$ (33,445)	$ (547,052)	$ 2,495,417	$ 6,416	$ 939