Loans - Risk Categories of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,059,323	$ 3,817,377
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,956,794	3,722,027
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	38,144	47,545
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	64,328	47,494
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	57	311
Real Estate | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	376,257	343,125
Real Estate | Construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	364,903	328,127
Real Estate | Construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	6,036	10,414
Real Estate | Construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	5,318	4,584
Real Estate | Construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real Estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,726,699	1,639,992
Real Estate | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,673,457	1,586,932
Real Estate | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	24,328	29,273
Real Estate | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	28,914	23,787
Real Estate | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real Estate | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,152,640	1,038,810
Real Estate | Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,126,238	1,023,925
Real Estate | Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,985	4,621
Real Estate | Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	23,417	10,203
Real Estate | Residential real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	61
Commercial and financial | Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	610,955	606,014
Commercial and financial | Commercial and financial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	602,973	593,689
Commercial and financial | Commercial and financial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,895	3,237
Commercial and financial | Commercial and financial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	6,030	8,838
Commercial and financial | Commercial and financial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	57	250
Consumer | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	192,772	189,436
Consumer | Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	189,223	189,354
Consumer | Consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,900	0
Consumer | Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	649	82
Consumer | Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0