Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Basic earnings per share [Abstract]
Net income		$ 69,191	$ 133,076
Weighted average common shares outstanding (in shares)		340,144	339,107
Basic income per share (in dollars per share)		$ 0.20	$ 0.39
Diluted earnings per share [Abstract]
Net income		$ 69,191	$ 133,076
Effect of dilutive securities [Abstract]
Diluted income available to common shareholders		$ 73,851	$ 149,582
Weighted-average shares - Basic (in shares)		340,144	339,107
Weighted-average shares - Diluted (in shares)		431,365	468,121
Diluted income per share (in dollars per share)		$ 0.17	$ 0.32
Antidilutive securities (in shares)		23,300	0
Effective income tax rate		35.00%
Unvested Restricted Stock Units
Effect of dilutive securities [Abstract]
Dilutive securities (in shares)		1,679	2,569
Convertible Senior Notes, interest at 2% per annum, due April 2020
Effect of dilutive securities [Abstract]
Dilutive securities	[1]	$ 1,982	$ 3,049
Dilutive securities (in shares)		71,917	71,917
Stated interest rate		2.00%
Convertible Senior Notes, interest at 5% per annum, due May 2017
Effect of dilutive securities [Abstract]
Dilutive securities	[1]	$ 2,678	$ 4,692
Dilutive securities (in shares)		17,625	25,674
Antidilutive securities (in shares)		10,300
Stated interest rate		5.00%
Convertible Junior Debentures at 9% per annum, Due 2063
Effect of dilutive securities [Abstract]
Dilutive securities	[1]	$ 0	$ 8,765
Dilutive securities (in shares)		0	28,854
Antidilutive securities (in shares)		9,800
Stated interest rate		9.00%

[1] Due to the valuation allowance recorded against deferred tax assets, the three months ended March 31, 2015 were not tax effected. The three months ended March 31, 2016 have been tax effected at a rate of 35%.