Loans - Risk Categories of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 4,986,289	$ 4,825,214
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,880,388	4,694,297
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	50,228	67,296
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	54,202	63,596
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,471	25
Construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	326,324	443,568
Construction and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	316,636	428,044
Construction and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4,559	10,429
Construction and land development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,129	5,095
Construction and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,310,367	2,132,066
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,260,472	2,063,589
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	27,838	41,429
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	21,736	27,048
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	321	0
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,409,946	1,324,377
Residential real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,386,760	1,296,634
Residential real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,978	3,654
Residential real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	19,208	24,089
Residential real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial and financial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	722,286	722,322
Commercial and financial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	703,565	707,663
Commercial and financial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,436	8,387
Commercial and financial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,135	6,247
Commercial and financial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,150	25
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	217,366	202,881
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	212,955	198,367
Consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,417	3,397
Consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	994	1,117
Consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0