Investment Securities (Amortized Cost and Approximate Fair Value of Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Gain (Loss) on Investments [Line Items]
Amortized Cost	$ 520,793	$ 498,104
Gross Unrealized Gains	18,218	21,184
Gross Unrealized Losses	6,144	5,945
Fair Value	532,867	513,343
Amortized Cost	336,696	361,020
Gross Unrealized Gains	14,807	17,170
Gross Unrealized Losses	64	16
Fair Value	351,439	378,174
Amortized Cost	857,489	859,124
Gross Unrealized Gains	33,025	38,354
Securities Gross Unrealized Losses	6,208	5,961
Fair Value	884,306	891,517
U.S. Government-sponsored agency securities
Gain (Loss) on Investments [Line Items]
Amortized Cost	4,228	4,475
Gross Unrealized Gains	159	165
Fair Value	4,387	4,640
State and municipal
Gain (Loss) on Investments [Line Items]
Amortized Cost	151,379	148,187
Gross Unrealized Gains	8,615	10,025
Gross Unrealized Losses	122	18
Fair Value	159,872	158,194
Amortized Cost	112,390	117,227
Gross Unrealized Gains	4,120	5,489
Gross Unrealized Losses	1	1
Fair Value	116,509	122,715
U.S. Government-sponsored mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Amortized Cost	357,307	337,631
Gross Unrealized Gains	9,444	10,994
Gross Unrealized Losses	216	46
Fair Value	366,535	348,579
Amortized Cost	224,306	243,793
Gross Unrealized Gains	10,687	11,681
Gross Unrealized Losses	63	15
Fair Value	234,930	255,459
Corporate obligations
Gain (Loss) on Investments [Line Items]
Amortized Cost	6,173	6,105
Gross Unrealized Losses	5,806	5,881
Fair Value	367	224
Equity Securities
Gain (Loss) on Investments [Line Items]
Amortized Cost	1,706	1,706
Fair Value	$ 1,706	$ 1,706

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Securities Gross Unrealized Gains

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

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As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

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