Earnings Per Share (Anti-dilutive Shares) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
3.00% convertible senior unsecured notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	0	16,992
Stated interest rates (as a percent)	3.00%
Series J convertible perpetual preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	15,635	15,635
1.50% convertible senior unsecured notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	0	11,567
Stated interest rates (as a percent)	1.50%
Joint venture shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	298	298