Loans - Risk Categories of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,974,016	$ 3,817,377
Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	359,070	343,125
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,701,295	1,639,992
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,103,945	1,038,810
Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	618,870	606,014
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	190,836	189,436
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,877,851	3,722,027
Pass | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	351,792	328,127
Pass | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,647,630	1,586,932
Pass | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,077,202	1,023,925
Pass | Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	612,333	593,689
Pass | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	188,894	189,354
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	30,065	47,545
Special Mention | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	6,456	10,414
Special Mention | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	19,716	29,273
Special Mention | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,341	4,621
Special Mention | Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	214	3,237
Special Mention | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	1,338	0
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	66,000	47,494
Substandard | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	822	4,584
Substandard | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	33,949	23,787
Substandard | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	24,402	10,203
Substandard | Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	6,223	8,838
Substandard | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	604	82
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	100	311
Doubtful | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Doubtful | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Doubtful | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	0	61
Doubtful | Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	100	250
Doubtful | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0