CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning 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		505,733,000
Increase (Decrease) in Stockholders' Equity
Net income	152,066			152,066
Other comprehensive income	1,451				1,451
Dividends declared on common stock	(163,120)			(163,120)
Issuances of common stock	3,219	$ 2,326	893
Issuances of common stock (in shares)		931,000
Share-based compensation	6,772		6,772
Ending balance at Mar. 31, 2015	10,214,870	$ 1,266,659	5,844,995	3,209,904	(106,688)
Balance (in shares) at Mar. 31, 2015		506,664,000
Beginning 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
Increase (Decrease) in Stockholders' Equity
Net income	$ 241,312			241,312
Other comprehensive income	1,145				1,145
Dividends declared on common stock	(173,619)			(173,619)
Issuances of common stock	(2,712)	$ 1,043	(3,755)
Purchase of common stock for settlement of equity awards	(789)		(789)
Issuances of common stock (in shares)		417,000
Share-based compensation	5,377		5,377
Ending balance at Mar. 31, 2016	$ 10,671,634	$ 1,269,882	$ 5,889,939	$ 3,620,421	$ (108,608)
Balance (in shares) at Mar. 31, 2016	507,952,795	507,953,000