Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 440,656	$ 430,525	$ 413,806	$ 400,075	$ 394,169	$ 389,189	$ 378,207	$ 301,356	$ 1,685,061	$ 1,462,921	$ 1,000,627
Income from continuing operations	142,530	241,001	172,197	103,420	88,209	(15,949)	334	(14,767)	659,148	57,827	250,431
Total discontinued operations	0	0	0	38,179	163,881	5,063	35,763	90,237	38,179	294,944	173,131
Net income attributable to common stockholders	$ 142,642	$ 241,100	$ 158,086	$ 141,739	$ 252,212	$ (10,715)	$ 36,218	$ 75,427	$ 683,567	$ 353,141	$ 423,869
Net income (loss) per common share - basic (in dollars per share)	$ 1.08	$ 1.83	$ 1.22	$ 1.09	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 5.22	$ 2.78	$ 4.34
Net income (loss) per common share - diluted (in dollars per share)	$ 1.08	$ 1.83	$ 1.21	$ 1.09	$ 1.95	$ (0.08)	$ 0.28	$ 0.63	$ 5.21	$ 2.78	$ 4.32