Securities (Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,496,167	$ 1,472,565
Gross Unrealized Gains	36,518	43,738
Gross Unrealized Losses	(8,116)	(10,228)
Estimated Fair Value	1,524,569	1,506,075
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,475,835	1,451,313
Gross Unrealized Gains	35,740	43,005
Gross Unrealized Losses	(8,116)	(10,228)
Estimated Fair Value	1,503,459	1,484,090
U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,885	21,002
Gross Unrealized Gains	289	443
Gross Unrealized Losses	0	(1)
Estimated Fair Value	8,174	21,444
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,049,782	1,027,234
Gross Unrealized Gains	16,230	19,002
Gross Unrealized Losses	(6,098)	(10,035)
Estimated Fair Value	1,059,914	1,036,201
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	418,168	403,077
Gross Unrealized Gains	19,221	23,560
Gross Unrealized Losses	(2,018)	(192)
Estimated Fair Value	435,371	426,445
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,332	21,252
Gross Unrealized Gains	778	733
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 21,110	$ 21,985

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

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details