Fair Value Measurements on a Recurring Basis (Details) (Recurring measurements, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financial Assets
Total assets measured at fair value on a recurring basis	$ 2,387,428us-gaap_AssetsFairValueDisclosure	$ 3,224,725us-gaap_AssetsFairValueDisclosure
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	16,668
Interest rate swaps
Financial Liabilities
Interest rate swaps	16,668
U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	44
U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	21,945	10,628
State and local governments
Financial Assets
Investment securities, available-for-sale	997,969	1,385,078
Corporate bonds
Financial Assets
Investment securities, available-for-sale	314,854	442,501
Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,052,616	1,384,622
Interest rate swaps
Financial Assets
Interest rate swaps		1,896
Level 1
Financial Assets
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0
Level 1 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	0
Level 1 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0
Level 1 \| U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 \| State and local governments
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 \| Corporate bonds
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 \| Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 \| Interest rate swaps
Financial Assets
Interest rate swaps		0
Level 2
Financial Assets
Total assets measured at fair value on a recurring basis	2,387,428	3,224,725
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	16,668
Level 2 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	16,668
Level 2 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	44
Level 2 \| U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	21,945	10,628
Level 2 \| State and local governments
Financial Assets
Investment securities, available-for-sale	997,969	1,385,078
Level 2 \| Corporate bonds
Financial Assets
Investment securities, available-for-sale	314,854	442,501
Level 2 \| Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,052,616	1,384,622
Level 2 \| Interest rate swaps
Financial Assets
Interest rate swaps		1,896
Level 3
Financial Assets
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0
Level 3 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	0
Level 3 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0
Level 3 \| U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 \| State and local governments
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 \| Corporate bonds
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 \| Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 \| Interest rate swaps
Financial Assets
Interest rate swaps		$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6505594

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Section 03

-Paragraph 1

-Subparagraph a, f, g

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