CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) (USD $) In Thousands, except Share data, unless otherwise specified	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	433,427			433,427
Other comprehensive income	818				818
Dividends declared on common stock	(274,308)			(274,308)
Issuances of common stock	243,125	23,340	219,785
Issuances of common stock (in shares)		9,336,000
Share-based compensation	23,106		23,106
Ending balance at Jun. 30, 2013	9,300,245	1,243,239	5,595,906	2,572,935	(111,835)
Balance (in shares) at Jun. 30, 2013		497,296,000
Beginning balance at Mar. 31, 2013	9,155,113	1,236,888	5,515,513	2,516,332	(113,620)
Balance (in shares) at Mar. 31, 2013		494,755,000
Increase (Decrease) in Stockholders' Equity
Net income	196,857			196,857
Other comprehensive income	1,785				1,785
Dividends declared on common stock	(140,254)			(140,254)
Issuances of common stock	74,291	6,351	67,940
Issuances of common stock (in shares)		2,541,000
Share-based compensation	12,453		12,453
Ending balance at Jun. 30, 2013	9,300,245	1,243,239	5,595,906	2,572,935	(111,835)
Balance (in shares) at Jun. 30, 2013		497,296,000
Beginning 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	497,971,508	497,972,000
Increase (Decrease) in Stockholders' Equity
Net income	456,385			456,385
Other comprehensive income	2,909				2,909
Dividends declared on common stock	(302,962)			(302,962)
Issuances of common stock	184,660	17,835	166,825
Issuances of common stock (in shares)		7,134,000
Share-based compensation	13,830		13,830
Ending balance at Jun. 30, 2014	9,920,772	1,262,764	5,799,968	2,961,406	(103,366)
Balance (in shares) at Jun. 30, 2014	505,105,562	505,106,000
Beginning balance at Mar. 31, 2014	9,747,424	1,252,879	5,681,150	2,918,215	(104,820)
Balance (in shares) at Mar. 31, 2014		501,152,000
Increase (Decrease) in Stockholders' Equity
Net income	195,164			195,164
Other comprehensive income	1,454				1,454
Dividends declared on common stock	(151,973)			(151,973)
Issuances of common stock	120,938	9,885	111,053
Issuances of common stock (in shares)		3,954,000
Share-based compensation	7,765		7,765
Ending balance at Jun. 30, 2014	$ 9,920,772	$ 1,262,764	$ 5,799,968	$ 2,961,406	$ (103,366)
Balance (in shares) at Jun. 30, 2014	505,105,562	505,106,000