Consolidated Statements of Equity - USD ($) $ in Thousands	Total		Total Stockholders' Equity	Preferred Stock [Member]	Common Stock	Common Stock Additional Paid-in Capital	Common Stock Distributions in Excess of Earnings	Noncontrolling Interests - Common Units of the Operating Partnership	Subsidiaries [Member]	Subsidiaries [Member] Noncontrolling Interests - Common Units of the Operating Partnership
Beginning Balance at Dec. 31, 2012	$ 2,235,933		$ 2,189,630	$ 192,411	$ 749	$ 2,126,005	$ (129,535)	$ 46,303
Beginning Balance, shares at Dec. 31, 2012					74,926,981
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,565		43,880				43,880	685	$ 44,565	$ 224
Issuance of common stock, shares (Note 10)					7,215,838
Issuance of share-based compensation awards, shares (Note 12)					0
Issuance of share-based compensation awards	1,448		1,448			1,448
Noncash amortization of share-based compensation	9,563		9,563			9,563			9,563
Exercise of stock options, shares					16,303
Issuance of common stock (Note 10)	349,951		349,951		$ 72	349,879
Exchange Of Common Units Of The Operating Partnership Into Shares Of The Companys Common Stock	0		450			(450)		450
Exercise of stock options	(128)		(128)			(128)
Noncontrolling Interest, Increase from Business Combination	4,885							4,885	4,885	4,885
Repurchase of common stock and restricted stock units (Note 12)	(2,521)		(2,521)			(2,521)
Repurchase of common stock and restricted stock units, shares (Note 12)					(42,896)
Settlement of restricted stock units for shares of common stock (Note 12)	1		1		$ 1	0			1
Settlement of restricted stock units for shares of common stock, shares (Note 12)					37,245
Exchange of common units of the Operating Partnership, shares (Note 10)					473
Adjustment for noncontrolling interest (Note 2)	0		(5,977)			5,977		(5,977)
Preferred distributions	(13,250)		(13,250)				(13,250)		(13,250)
Dividends declared per common share and common unit ($1.40 per share/ unit for 2010, 2011 and $1.63 per share/unit for 2009)	(114,543)		(111,991)				(111,991)	(2,552)
Ending Balance at Dec. 31, 2013	2,516,160		2,461,312	192,411	$ 822	2,478,975	(210,896)	54,848
Ending Balance, shares at Dec. 31, 2013					82,153,944
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	183,808		180,219				180,219	3,589	183,808	260
Issuance of common stock, shares (Note 10)					1,950,599
Issuance of share-based compensation awards	1,692		1,692			1,692
Noncash amortization of share-based compensation	14,471		14,471			14,471			14,471
Exercise of stock options, shares					495,000
Issuance of common stock (Note 10)	123,860		123,860		$ 20	123,840
Exercise of stock options	(21,092)		(21,092)		$ (5)	(21,087)
Noncontrolling Interest, Increase from Business Combination	977							977	977	977
Repurchase of common stock and restricted stock units (Note 12)	(3,533)		(3,533)			(3,533)
Repurchase of common stock and restricted stock units, shares (Note 12)					(58,045)
Settlement of restricted stock units for shares of common stock (Note 12)	(1)		(1)		$ 0	(1)
Stock Issued During Period, Shares, in Connection with Early Exchange of Notes					2,091,323
Stock Issued During Period, Value, in Connection with Early Exchange of Notes	223		223		$ 21	202			$ 223
Stock Received During Period, Call Options					515,342				0
Stock Issued During Period, Value, Capped Call Option Transactions	0		0		$ (5)	5
Shares of Common stock exercised in the capped call option					111,206
Settlement of restricted stock units for shares of common stock, shares (Note 12)					141,205
Exchange of common units of the Operating Partnership (Note 10)	0		28			28		(28)
Exchange of common units of the Operating Partnership, shares (Note 10)					1,000
Adjustment for noncontrolling interest (Note 2)	0		866			866		(866)
Preferred distributions	(13,250)		(13,250)				(13,250)		$ (13,250)
Dividends declared per common share and common unit ($1.40 per share/ unit for 2010, 2011 and $1.63 per share/unit for 2009)	(121,563)		(119,037)				(119,037)	(2,526)
Ending Balance at Dec. 31, 2014	$ 2,723,936		2,666,210	192,411	$ 863	2,635,900	(162,964)	57,726
Ending Balance, shares at Dec. 31, 2014	86,259,684	[1]			86,259,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 238,604		234,081				234,081	4,523	238,604	467
Issuance of common stock, shares (Note 10)					5,640,033
Issuance of share-based compensation awards	1,692		1,692			1,692
Noncash amortization of share-based compensation	18,869		18,869			18,869			18,869
Exercise of stock options, shares					342,000
Issuance of common stock (Note 10)	387,398		387,398		$ 56	387,342
Exercise of stock options	(14,573)		(14,573)		(4)	(14,569)
Noncontrolling Interest, Increase from Business Combination	474							474	474	$ 474
Repurchase of common stock and restricted stock units (Note 12)	(7,081)		(7,081)		$ 0	(7,081)
Repurchase of common stock and restricted stock units, shares (Note 12)					(101,389)
Settlement of restricted stock units for shares of common stock (Note 12)	(1)		(1)		$ 0	(1)
Settlement of restricted stock units for shares of common stock, shares (Note 12)					78,937
Exchange of common units of the Operating Partnership (Note 10)	0		1,223			1,223		(1,223)
Exchange of common units of the Operating Partnership, shares (Note 10)					39,425
Adjustment for noncontrolling interest (Note 2)	0		4,619			4,619		(4,619)
Preferred distributions	(13,250)		(13,250)				(13,250)		$ (13,250)
Dividends declared per common share and common unit ($1.40 per share/ unit for 2010, 2011 and $1.63 per share/unit for 2009)	(130,628)		(128,129)				(128,129)	(2,499)
Ending Balance at Dec. 31, 2015	$ 3,234,586		$ 3,170,966	$ 192,411	$ 923	$ 3,047,894	$ (70,262)	$ 63,620
Ending Balance, shares at Dec. 31, 2015	92,258,690	[1]			92,258,690

[1] The amount includes nonvested shares.