Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Investment securities [Abstract]
Investment securities, fair value	$ 615,194	$ 528,458	$ 451,443
Real estate and other repossessed assets, Valuation allowance	$ 36,004	$ 36,873	$ 30,408
Shareholders' equity: [Abstract]
Common stock, par value (in dollars per share)	$ 0.00006	$ 0.00006	$ 0.00006
Common stock, shares authorized (in shares)	2,500,000,000	2,500,000,000	2,500,000,000
Common stock, shares issued (in shares)	72,945,798	72,415,346	71,902,099
Common stock, shares outstanding (in shares)	72,945,798	72,415,346	71,902,099
Treasury stock, shares at cost (in shares)	4,258,080	4,087,995	3,785,206