Allowance for Loan Losses - Loan Portfolio and Related Allowance (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Recorded Investment
Individually Evaluated for Impairment	$ 30,291	$ 32,718
Collectively Evaluated for Impairment	24,720	20,946
Total	3,799,961	2,853,544
Associated Allowance
Individually Evaluated for Impairment	2,402	2,454
Collectively Evaluated for Impairment	3,769,670	2,820,826
Total	27,122	23,400
PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	17,417	12,996
Associated Allowance
Individually Evaluated for Impairment	0	0
Construction and Land Development [Member]
Recorded Investment
Individually Evaluated for Impairment	474	277
Collectively Evaluated for Impairment	1,619	1,219
Total	342,004	160,116
Associated Allowance
Individually Evaluated for Impairment	23	0
Collectively Evaluated for Impairment	341,530	159,839
Total	1,642	1,219
Construction and Land Development [Member] \| PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	1,121	114
Associated Allowance
Individually Evaluated for Impairment	0	0
Commercial Real Estate [Member]
Recorded Investment
Individually Evaluated for Impairment	8,255	10,204
Collectively Evaluated for Impairment	9,090	8,878
Total	1,630,215	1,334,480
Associated Allowance
Individually Evaluated for Impairment	195	395
Collectively Evaluated for Impairment	1,621,960	1,324,276
Total	9,285	9,273
Commercial Real Estate [Member] \| PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	9,776	11,257
Associated Allowance
Individually Evaluated for Impairment	0	0
Residential Real Estate [Member]
Recorded Investment
Individually Evaluated for Impairment	18,720	22,038
Collectively Evaluated for Impairment	6,040	5,424
Total	1,033,185	835,789
Associated Allowance
Individually Evaluated for Impairment	1,091	2,059
Collectively Evaluated for Impairment	1,014,465	813,751
Total	7,131	7,483
Residential Real Estate [Member] \| PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	5,626	684
Associated Allowance
Individually Evaluated for Impairment	0	0
Commercial And Financial [Member]
Recorded Investment
Individually Evaluated for Impairment	2,455	199
Collectively Evaluated for Impairment	6,247	3,636
Total	605,121	368,707
Associated Allowance
Individually Evaluated for Impairment	1,050	0
Collectively Evaluated for Impairment	602,666	368,508
Total	7,297	3,636
Commercial And Financial [Member] \| PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	894	941
Associated Allowance
Individually Evaluated for Impairment	0	0
Consumer [Member]
Recorded Investment
Individually Evaluated for Impairment	387	0
Collectively Evaluated for Impairment	1,724	1,789
Total	189,436	154,452
Associated Allowance
Individually Evaluated for Impairment	43	0
Collectively Evaluated for Impairment	189,049	154,452
Total	1,767	1,789
Consumer [Member] \| PCI Loans [Member]
Recorded Investment
Individually Evaluated for Impairment	0	0
Associated Allowance
Individually Evaluated for Impairment	$ 0	$ 0

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A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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The balance of financing receivables 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
-Topic 310
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The balance of financing receivables that were individually evaluated for impairment.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

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