Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Investment securities [Abstract]
Investment securities, fair value	$ 643,091	$ 673,626	$ 676,445
Real estate and other repossessed assets, Valuation allowance	$ 12,874	$ 22,937	$ 25,916
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)	74,461,234	74,003,754	73,964,496
Common stock, shares outstanding (in shares)	74,461,234	74,003,754	73,964,496
Treasury stock, shares at cost (in shares)	6,748,203	4,890,018	4,626,998