Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Investment securities [Abstract]
Investment securities, fair value	$ 657,971	$ 673,626	$ 685,063
Real estate and other repossessed assets, Valuation allowance	$ 18,886	$ 22,937	$ 23,555
Shareholders' equity: [Abstract]
Common stock, par value (in dollars per share)	$ 0.00006	$ 0.00006	$ 0.00006
Common stock, shares authorized (in shares)	2,500,000,000us-gaap_CommonStockSharesAuthorized	2,500,000,000us-gaap_CommonStockSharesAuthorized	2,500,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued (in shares)	74,351,392us-gaap_CommonStockSharesIssued	74,003,754us-gaap_CommonStockSharesIssued	73,547,801us-gaap_CommonStockSharesIssued
Common stock, shares outstanding (in shares)	74,351,392us-gaap_CommonStockSharesOutstanding	74,003,754us-gaap_CommonStockSharesOutstanding	73,547,801us-gaap_CommonStockSharesOutstanding
Treasury stock, shares at cost (in shares)	5,429,078us-gaap_TreasuryStockShares	4,890,018us-gaap_TreasuryStockShares	4,407,591us-gaap_TreasuryStockShares

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Face amount or stated value per share of common stock.

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Fair value of investments in debt securities classified as held-to-maturity.

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For each period for which an income statement is required, disclosure of the changes in the allowance, including balances at end of period.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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