Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$ 486,624	$ 442,488
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000us-gaap_PreferredStockSharesAuthorized	5,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value (usd per share)	$ 5.00	$ 5.00
Common stock, shares authorized	75,000,000us-gaap_CommonStockSharesAuthorized	75,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	32,656,166us-gaap_CommonStockSharesIssued	32,656,166us-gaap_CommonStockSharesIssued
Common stock, shares outstanding	31,604,937us-gaap_CommonStockSharesOutstanding	31,545,145us-gaap_CommonStockSharesOutstanding

Face amount or stated value per share of common stock.

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