Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Investment securities [Abstract]
Investment securities, fair value	$ 625,705	$ 528,458	$ 440,638
Real estate and other repossessed assets, Valuation allowance	$ 26,837	$ 36,873	$ 32,730
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)	73,029,101	72,415,346	72,006,628
Common stock, shares outstanding (in shares)	73,029,101	72,415,346	72,006,628
Treasury stock, shares at cost (in shares)	4,289,893	4,087,995	3,862,469