Earnings (loss) per share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Basic earnings per share [Abstract]
Average common shares outstanding (in shares)	201,097,000	181,267,000	200,921,000	152,344,000
Net (loss) income	$ (151,732)	$ 24,551	$ (185,393)	$ (125,540)
Basic (loss) earnings per share (in dollars per share)	$ (0.75)	$ 0.14	$ (0.92)	$ (0.82)
Diluted earnings per share [Abstract]
Weighted-average shares - Basic (in shares)	201,097,000	181,267,000	200,921,000	152,344,000
Common stock equivalents (in shares)	0	889,000	0	0
Weighted-average shares - Diluted (in shares)	201,097,000	182,156,000	200,921,000	152,344,000
Net (loss) income	$ (151,732)	$ 24,551	$ (185,393)	$ (125,540)
Diluted (loss) earnings per share (in dollars per share)	$ (0.75)	$ 0.13	$ (0.92)	$ (0.82)
Participating Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive participating securities excluded from EPS calculation (in shares)	1,000,000		1,200,000	1,800,000
Participating securities with non-forfeitable rights to dividends included in basic EPS (in shares)		1,800,000
Common Stock Equivalents [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive participating securities excluded from EPS calculation (in shares)	55,500,000	53,300,000	55,500,000	45,800,000