Fair Value Measurements on a Recurring Basis (Details) - Recurring Measurements - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial Assets
Total assets measured at fair value on a recurring basis	$ 2,604,625	$ 2,610,760
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	27,598	19,499
Interest rate swaps
Financial Liabilities
Interest rate swaps	27,598	19,499
U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	45,687	47,451
U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	68,773	93,167
State and local governments
Financial Assets
Investment securities, available-for-sale	901,133	885,019
Corporate bonds
Financial Assets
Investment securities, available-for-sale	442,875	384,163
Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,146,157	1,200,960
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	2,604,625	2,610,760
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	27,598	19,499
Level 2 \| Interest rate swaps
Financial Liabilities
Interest rate swaps	27,598	19,499
Level 2 \| U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	45,687	47,451
Level 2 \| U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	68,773	93,167
Level 2 \| State and local governments
Financial Assets
Investment securities, available-for-sale	901,133	885,019
Level 2 \| Corporate bonds
Financial Assets
Investment securities, available-for-sale	442,875	384,163
Level 2 \| Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	1,146,157	1,200,960
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)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Subparagraph a, f, g
-Article 7

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