Fair Value Measurements Recurring Basis (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Assets:
Available-for-sale securities:	$ 981,951,000	$ 994,065,000
Equity securities	7,491,000	14,228,000
U.S. government and agencies
Assets:
Available-for-sale securities:	24,441,000	29,114,000
Government-sponsored entities
Assets:
Available-for-sale securities:	199,600,000	207,703,000
Municipal bonds
Assets:
Available-for-sale securities:	312,629,000	308,959,000
Mortgage-backed securities
Assets:
Available-for-sale securities:	445,281,000	448,289,000
Fair Value, Measurements, Recurring
Assets:
Available-for-sale securities:	981,951,000	994,065,000
Trading securities held in the “rabbi trust”	7,705,000	6,839,000
Liabilities:
Deferred compensation “rabbi trust”	7,705,000	6,839,000
Fair Value, Measurements, Recurring \| U.S. government and agencies
Assets:
Available-for-sale securities:	24,441,000	29,114,000
Fair Value, Measurements, Recurring \| Government-sponsored entities
Assets:
Available-for-sale securities:	199,600,000	207,703,000
Fair Value, Measurements, Recurring \| Municipal bonds
Assets:
Available-for-sale securities:	312,629,000	308,959,000
Fair Value, Measurements, Recurring \| Mortgage-backed securities
Assets:
Available-for-sale securities:	445,281,000	448,289,000
Fair Value, Measurements, Recurring \| Interest rate customer products
Assets:
Derivatives	23,609,000	21,889,000
Liabilities:
Derivatives	24,296,000	22,385,000
Fair Value, Measurements, Recurring \| Interest rate swap
Assets:
Derivatives	205,000	553,000
Fair Value, Measurements, Recurring \| Risk participation agreements
Assets:
Derivatives	138,000	2,000
Liabilities:
Derivatives	184,000	152,000
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1)
Assets:
Available-for-sale securities:	0	0
Equity securities	7,491,000	14,228,000
Trading securities held in the “rabbi trust”	7,705,000	6,839,000
Liabilities:
Deferred compensation “rabbi trust”	7,705,000	6,839,000
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| U.S. government and agencies
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Government-sponsored entities
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Municipal bonds
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Mortgage-backed securities
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Interest rate customer products
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Interest rate swap
Assets:
Derivatives	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (Level 1) \| Risk participation agreements
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2)
Assets:
Available-for-sale securities:	981,951,000	994,065,000
Equity securities	0	0
Trading securities held in the “rabbi trust”	0	0
Liabilities:
Deferred compensation “rabbi trust”	0	0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| U.S. government and agencies
Assets:
Available-for-sale securities:	24,441,000	29,114,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Government-sponsored entities
Assets:
Available-for-sale securities:	199,600,000	207,703,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Municipal bonds
Assets:
Available-for-sale securities:	312,629,000	308,959,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Mortgage-backed securities
Assets:
Available-for-sale securities:	445,281,000	448,289,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Interest rate customer products
Assets:
Derivatives	23,609,000	21,889,000
Liabilities:
Derivatives	24,296,000	22,385,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Interest rate swap
Assets:
Derivatives	205,000	553,000
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Risk participation agreements
Assets:
Derivatives	138,000	2,000
Liabilities:
Derivatives	184,000	152,000
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets:
Available-for-sale securities:	0	0
Equity securities	0	0
Trading securities held in the “rabbi trust”	0	0
Liabilities:
Deferred compensation “rabbi trust”	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| U.S. government and agencies
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Government-sponsored entities
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Municipal bonds
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Mortgage-backed securities
Assets:
Available-for-sale securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Interest rate customer products
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Interest rate swap
Assets:
Derivatives	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Risk participation agreements
Assets:
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 35
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of financial and nonfinancial obligations.

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