Loans and Allowance for Loan Losses - Disaggregated analysis of activity in the allowance for acquired credit impaired loans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Reduction due to loan removals	$ (180)	$ (243)	$ (886)	$ (346)
Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	1,829	2,300	1,829	2,300
Loans collectively evaluated for impairment	46,045	37,849	46,045	37,849
Loans:
Loans individually evaluated for impairment	62,593	49,120	62,593	49,120
Loans collectively evaluated for impairment	7,134,946	5,943,273	7,134,946	5,943,273
Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	4,084	4,556	4,627	3,395
Provision (benefit) for loan losses	522	(572)	685	692
Reduction due to loan removals	(180)	(243)	(886)	(346)
Balance at the end of the period	4,426	3,741	4,426	3,741
Loans collectively evaluated for impairment	4,426	3,741	4,426	3,741
Loans:
Loans collectively evaluated for impairment	556,405	606,222	556,405	606,222
Carrying value	556,405	606,222	556,405	606,222	$ 623,430
Residential real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	2,509	3,108	3,553	2,419
Provision (benefit) for loan losses	137	(192)	(807)	559
Reduction due to loan removals	(132)	(175)	(232)	(237)
Balance at the end of the period	2,514	2,741	2,514	2,741
Loans collectively evaluated for impairment	2,514	2,741	2,514	2,741
Loans:
Loans collectively evaluated for impairment	229,502	256,602	229,502	256,602
Carrying value	229,502	256,602	229,502	256,602	260,787
Commercial non-owner occupied real estate \| Construction and land development \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	846	1,310	846	1,310
Loans collectively evaluated for impairment	5,341	4,436	5,341	4,436
Loans:
Loans individually evaluated for impairment	42,392	30,037	42,392	30,037
Loans collectively evaluated for impairment	864,498	682,205	864,498	682,205
Commercial non-owner occupied real estate \| Construction and land development \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	215	130	180	139
Provision (benefit) for loan losses	390		478	(3)
Reduction due to loan removals	(29)	(38)	(82)	(44)
Balance at the end of the period	576	92	576	92
Loans collectively evaluated for impairment	576	92	576	92
Loans:
Loans collectively evaluated for impairment	40,951	52,977	40,951	52,977
Carrying value	40,951	52,977	40,951	52,977	49,649
Commercial non-owner occupied real estate \| Other commercial non-owner occupied real estate \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	93	146	93	146
Loans collectively evaluated for impairment	7,116	6,018	7,116	6,018
Loans:
Loans individually evaluated for impairment	1,348	754	1,348	754
Loans collectively evaluated for impairment	1,133,887	952,157	1,133,887	952,157
Commercial non-owner occupied real estate \| Other commercial non-owner occupied real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	261	335	288	41
Provision (benefit) for loan losses	375	(292)	361
Reduction due to loan removals		(3)	(13)	(1)
Balance at the end of the period	636	40	636	40
Loans collectively evaluated for impairment	636	40	636	40
Loans:
Loans collectively evaluated for impairment	227,739	214,795	227,739	214,795
Carrying value	227,739	214,795	227,739	214,795	234,595
Consumer real estate \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	594	589	461	558
Provision (benefit) for loan losses	(19)	(37)	114
Reduction due to loan removals	(3)	(4)	(3)	(10)
Balance at the end of the period	572	548	572	548
Loans collectively evaluated for impairment	572	548	572	548
Loans:
Loans collectively evaluated for impairment	45,633	56,362	45,633	56,362
Carrying value	45,633	56,362	45,633	56,362
Consumer real estate \| Home equity loans \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	180	119	180	119
Loans collectively evaluated for impairment	3,188	3,128	3,188	3,128
Loans:
Loans individually evaluated for impairment	3,144	2,626	3,144	2,626
Loans collectively evaluated for impairment	453,802	408,906	453,802	408,906
Commercial and industrial \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	485	362	485	362
Loans collectively evaluated for impairment	6,226	4,781	6,226	4,781
Loans:
Loans individually evaluated for impairment	1,834	1,198	1,834	1,198
Loans collectively evaluated for impairment	939,233	761,385	939,233	761,385
Commercial and industrial \| Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	505	394	145	238
Provision (benefit) for loan losses	(361)	(51)	539	136
Reduction due to loan removals	(16)	(23)	(556)	(54)
Balance at the end of the period	128	320	128	320
Loans collectively evaluated for impairment	128	320	128	320
Loans:
Loans collectively evaluated for impairment	12,580	25,486	12,580	25,486
Carrying value	12,580	25,486	12,580	25,486	26,946
Other income producing property \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	144	238	144	238
Loans collectively evaluated for impairment	1,269	1,141	1,269	1,141
Loans:
Loans individually evaluated for impairment	3,240	3,641	3,240	3,641
Loans collectively evaluated for impairment	202,267	185,685	202,267	185,685
Consumer \| Non-acquired loans
Allowance for loan losses:
Loans individually evaluated for impairment	7	6	7	6
Loans collectively evaluated for impairment	3,064	2,526	3,064	2,526
Loans:
Loans individually evaluated for impairment	257	235	257	235
Loans collectively evaluated for impairment	416,393	357,526	416,393	357,526
Consumer \| Acquired credit impaired loans
Loans:
Carrying value	$ 45,633	$ 56,362	$ 45,633	$ 56,362	$ 51,453

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The sum of the periodic provision charged to earnings before adjustment for amounts covered under loss sharing agreement.

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No definition available.

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Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(2)
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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The increase (decrease) in the allowance for credit losses related to financing receivables.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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