Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Investment securities
Investment securities, fair value	$ 440,638	$ 462,657	$ 369,247
Shareholders' equity:
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)	72,006,628	71,533,354	71,100,444
Common stock, shares outstanding (in shares)	72,006,628	71,533,354	71,100,444
Treasury stock, shares at cost (in shares)	3,862,469	3,380,310	2,637,575