Quarterly Financial Information (Unaudited) (Restatement Amounts for Discontinued Operations Adjustment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Revenues	$ 841,274	$ 827,606	$ 811,920	$ 805,598	$ 732,090	$ 704,932	$ 674,529	$ 665,262	$ 3,286,398	$ 2,776,813	$ 2,516,617
Income from continuing operations attributable to common stockholders			131,578	102,868	86,481	90,961	107,617	90,973	406,740	376,032	374,338
Discontinued operations	$ (2,331)	$ (22,383)	18,243	17,574	20,709	18,171	30,781	30,074	$ 11,103	$ 99,735	$ 79,171
Previously Reported
Quarterly Financial Data [Abstract]
Revenues			891,322	884,024	803,987	779,035	751,254	741,470
Income from continuing operations attributable to common stockholders			149,754	120,865	107,601	109,391	138,653	118,016
Discontinued operations			67	(423)	(411)	(259)	(255)	3,031
Restatement Adjustment
Quarterly Financial Data [Abstract]
Revenues			(79,402)	(78,426)	(71,897)	(74,103)	(76,725)	(76,208)
Income from continuing operations attributable to common stockholders			$ (18,176)	$ (17,997)	$ (21,120)	$ (18,430)	$ (31,036)	$ (27,043)