Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Investment securities [Abstract]
Investment Securities, fair value	$ 489,895	$ 565,493	$ 580,310
Allowance for real estate and other repossessed assets	$ 11,738	$ 9,562	$ 9,524
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)	75,129,535	74,993,407	74,866,429
Common stock, shares outstanding (in shares)	75,129,535	74,993,407	74,866,429
Treasury stock, shares at cost (in shares)	9,672,749	9,655,975	8,955,975