Fair Value Measurements on a Recurring Basis (Details) - Recurring Measurements - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial Assets
Total assets measured at fair value on a recurring basis	$ 2,530,994	$ 2,387,428
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	23,623	16,668
Interest rate swaps
Financial Liabilities
Interest rate swaps	23,623	16,668
U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	49,315	44
U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	98,791	21,945
State and local governments
Financial Assets
Investment securities, available-for-sale	931,000	997,969
Corporate bonds
Financial Assets
Investment securities, available-for-sale	360,811	314,854
Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,091,077	1,052,616
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	0
Level 1 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	0	0
Level 1 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0	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 2
Financial Assets
Total assets measured at fair value on a recurring basis	2,530,994	2,387,428
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	23,623	16,668
Level 2 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	23,623	16,668
Level 2 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	49,315	44
Level 2 \| U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	98,791	21,945
Level 2 \| State and local governments
Financial Assets
Investment securities, available-for-sale	931,000	997,969
Level 2 \| Corporate bonds
Financial Assets
Investment securities, available-for-sale	360,811	314,854
Level 2 \| Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,091,077	1,052,616
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	0
Level 3 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	0	0
Level 3 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0	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

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

-Subparagraph (a)

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+ References

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

-Publisher FASB

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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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

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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

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-Name Accounting Standards Codification

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Subparagraph a, f, g

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