CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2012	$ 8,874,077	$ 1,219,899	$ 5,353,015	$ 2,413,816	$ (112,653)
Balance (in shares) at Dec. 31, 2012		487,960,000
Increase (Decrease) in Stockholders' Equity
Net income	948,234			948,234
Other comprehensive income (loss)	6,378				6,378
Dividends declared on common stock	(554,067)			(554,067)
Issuances of common stock	262,701	$ 25,030	237,671
Issuances of common stock (in shares)		10,012,000
Share-based compensation	28,627		28,627
Ending balance at Dec. 31, 2013	9,565,950	$ 1,244,929	5,619,313	2,807,983	(106,275)
Balance (in shares) at Dec. 31, 2013		497,972,000
Increase (Decrease) in Stockholders' Equity
Net income	1,021,306			1,021,306
Other comprehensive income (loss)	(1,864)				(1,864)
Dividends declared on common stock	(608,331)			(608,331)
Issuances of common stock	204,549	$ 19,404	185,145
Issuances of common stock (in shares)		7,761,000
Share-based compensation	32,872		32,872
Ending balance at Dec. 31, 2014	$ 10,214,482	$ 1,264,333	5,837,330	3,220,958	(108,139)
Balance (in shares) at Dec. 31, 2014	505,733,267	505,733,000
Increase (Decrease) in Stockholders' Equity
Net income	$ 984,485			984,485
Other comprehensive income (loss)	(1,614)				(1,614)
Dividends declared on common stock	(652,715)			(652,715)
Issuances of common stock	32,523	$ 4,506	28,017
Issuances of common stock (in shares)		1,803,000
Share-based compensation	23,759		23,759
Ending balance at Dec. 31, 2015	$ 10,600,920	$ 1,268,839	$ 5,889,106	$ 3,552,728	$ (109,753)
Balance (in shares) at Dec. 31, 2015	507,535,523	507,536,000