Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Statement of Financial Position [Abstract]
Investment securities - held-to-maturity, fair value	$ 899,653	$ 903,935	$ 812,914
Preferred stock, shares authorized	2,000,000us-gaap_PreferredStockSharesAuthorized	2,000,000us-gaap_PreferredStockSharesAuthorized	2,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, stated value	$ 1.00	$ 1.00	$ 1.00
Authorized and unissued common shares reserved for issuance	150,000,000us-gaap_CommonStockSharesAuthorized	150,000,000us-gaap_CommonStockSharesAuthorized	150,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	116,983,000us-gaap_CommonStockSharesIssued	116,847,000us-gaap_CommonStockSharesIssued	100,084,000us-gaap_CommonStockSharesIssued
Common stock, shares outstanding	116,983,000us-gaap_CommonStockSharesOutstanding	116,847,000us-gaap_CommonStockSharesOutstanding	100,084,000us-gaap_CommonStockSharesOutstanding

Face amount or stated value per share of common stock.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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