Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Investment securities
Investment securities, fair value	$ 460,358	$ 462,657	$ 483,234
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)	72,223,473	71,533,354	71,154,137
Common stock, shares outstanding (in shares)	72,223,473	71,533,354	71,154,137
Treasury stock, shares at cost (in shares)	4,008,119	3,380,310	3,147,747