Acquisitions Schedule of Consideration Paid, Assets Acquired and Liabilities Assumed in Acquisition of FCB (Details) - USD ($) $ in Thousands	Apr. 01, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill		$ 15,464		$ 10,990
As Recorded By Summit [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 48,116
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	54,042
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	101,317
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Securities Available for Sale	295
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Purchased Performing Loans	222,116
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Purchased Performing Loans	(2,693)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Purchased Credit Impaired Loans	3,627
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Purchased Credit Impaired Loans	(540)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets, Allowance For Loan Losses	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Allowance For Loan Losses	2,511
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	6,174
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Property, Plant, And Equipment	(4,222)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property Held-For-Sale	2,377
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Property Held-For-Sale	(2,219)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Goodwill	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Goodwill	(5,183)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	10,612
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Intangibles	10,612
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	5,102
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Other Assets	652
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	405,367
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Assets	(787)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	350,533
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Deposits	807
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	11,162
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Other Liabilities	(54)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	361,695
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Liabilities	753
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	43,672
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fair Value Adjustment, Assets (Liabilities), Net	(1,540)
Goodwill	4,444
First Century Bankshares, Inc [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	54,042
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	101,022
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Purchased Performing Loans	224,809
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Purchased Credit Impaired Loans	4,167
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets, Allowance For Loan Losses	(2,511)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	10,396
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property Held-For-Sale	4,596
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Goodwill	5,183
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	4,450
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	406,154		$ 406,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	349,726
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	11,216
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	360,942		$ 361,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	45,212
Goodwill	4,440
Cash Consideration [Domain] | As Recorded By Summit [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	14,989
Cash Consideration [Domain] | First Century Bankshares, Inc [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	15,000
Stock Consideration [Domain] | As Recorded By Summit [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	33,127
Stock Consideration [Domain] | First Century Bankshares, Inc [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 33,100