Common Stock - Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 128,068	$ (60,036)	$ 249,082	$ 94,581
Effect of dilutive securities:
Dilutive net income available to stockholders	$ 128,068	$ (60,036)	$ 249,082	$ 94,581
Weighted average basic shares	1,026,841,087	1,026,404,030	1,026,804,427	1,026,308,073
Effect of dilutive securities	663,943	791,374	695,546	822,063
Weighted average dilutive shares	1,027,505,030	1,027,195,404	1,027,499,973	1,027,130,136
Net income per average share attributable to common stockholders - Basic	$ 0.12	$ (0.06)	$ 0.24	$ 0.09
Net income per average share attributable to common stockholders - Diluted	$ 0.12	$ (0.06)	$ 0.24	$ 0.09