Employee Benefit Plans (Assumptions Used) (Details)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
BancShares Plan
Assumptions used to determine the benefit obligations
Discount rate	4.30%	4.68%
Rate of compensation increase	4.00%	4.00%
Assumptions used to determine net periodic benefit cost
Discount rate	4.68%	4.27%	4.90%
Rate of compensation increase	4.00%	4.00%	4.00%
Expected long-term rate of return on plan assets (percent)	7.50%	7.50%	7.50%
Bancorporation Plan
Assumptions used to determine the benefit obligations
Discount rate	4.30%	4.68%
Rate of compensation increase	4.00%	4.00%
Assumptions used to determine net periodic benefit cost
Discount rate	4.68%	4.27%	4.35%
Rate of compensation increase	4.00%	4.00%	4.00%
Expected long-term rate of return on plan assets (percent)	7.50%	7.50%	7.50%

The interest rate used to adjust for the time value of money for the plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

The interest rate used to adjust for the time value of money.

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Long-Term Rate of Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512046

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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Expected rate of compensation increases (for pay-related plans).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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