Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Investment securities [Abstract]
Investment Securities, fair value	$ 403,384	$ 480,035	$ 515,675
Allowance for real estate and other repossessed assets	$ 17,656	$ 12,648	$ 8,576
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)	75,313,559	75,147,686	75,089,152
Common stock, shares outstanding (in shares)	75,313,559	75,147,686	75,089,152
Treasury stock, shares at cost (in shares)	9,874,469	9,752,749	9,672,749