Investment Securities (Amortized Cost And Estimated Fair Value Of Investments In Debt Securities By Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value	$ 1,166,562	$ 1,258,139
Securities Held-to-Maturity, Amortized Cost	342,665	259,833
Securities held-to-maturity, fair value	347,110	256,672
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	283,718
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	287,175
Securities Held-to-Maturity, Amortized Cost	283,718	188,622
Securities held-to-maturity, fair value	$ 287,175	184,451
Held to Maturity Securities weighted avg yield	4.47%
Obligations Of U.S. Treasury And Other U.S. Government Sponsored Entities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	$ 75,000
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	$ 74,930
Available for Sale Securities Debt Maturities next twelve months Weighted Avg Yield	1.02%
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	$ 195,000
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	$ 193,911
Available for Sale Securities Debt Maturities two through five Weighted Avg Yield	1.25%
Securities Available-for-Sale, Total, Amortized cost	$ 270,000
Securities Available-for-Sale, Total Fair value	$ 268,841	267,533
Available for Sale Securities Weighted Avg Yield	1.18%
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total, Amortized cost	$ 892,784
Securities Available-for-Sale, Total Fair value	$ 893,705	987,172
Available for Sale Securities Weighted Avg Yield	2.09%
Securities Held-to-Maturity, Amortized Cost	$ 58,947	71,211
Securities held-to-maturity, fair value	$ 59,935	$ 72,221
Held to Maturity Securities weighted avg yield	3.20%

Available for Sale Securities Debt Maturities Years Two through Five Weighted Avg Yield

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Available for Sale Securities Debt Maturities next twelve months Weighted Avg Yield

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Available for Sale Securities Weighted Avg Yield

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Held to Maturity Securities weighted avg yield

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This item represents the cost of debt 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.

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

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of held-to-maturity debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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

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Amortized cost of held-to-maturity debt securities maturing after the tenth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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