Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investment securities [Abstract]
Investment securities, fair value	$ 629,159	$ 673,626
Real estate and other repossessed assets, allowance	$ 12,622	$ 22,937
Shareholders' equity: [Abstract]
Common stock, par value (in dollars per share)	$ 0.00006	$ 0.00006
Common stock, authorized (in shares)	2,500,000,000	2,500,000,000
Common stock, shares issued (in shares)	74,530,364	74,003,754
Common stock, shares outstanding (in shares)	74,530,364	74,003,754
Treasury stock, shares at cost (in shares)	8,636,332	4,890,018