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
Basic earnings per share:
Net income	$ 84,050	$ 78,982	$ 242,498	$ 213,749
Less preferred stock dividends	(2,070)	0	(2,070)	0
Net income available to common shareholders	81,980	78,982	240,428	213,749
Weighted average shares	98,233,589	75,743,002	91,296,338	70,057,263
Basic earnings per share	$ 0.83	$ 1.04	$ 2.63	$ 3.05
Diluted earnings per share:
Net income	84,050	78,982	242,498	213,749
Less preferred stock dividends for antidilutive shares	(2,070)	0	(2,070)	0
Net income available to common shareholders	$ 81,980	$ 78,982	$ 240,428	$ 213,749
Weighted average shares	98,233,589	75,743,002	91,296,338	70,057,263
Potential dilutive shares from exercise of stock options
Diluted weighted average shares	98,233,589	75,743,002	91,296,338	70,057,263
Diluted earnings per share	$ 0.83	$ 1.04	$ 2.63	$ 3.05