Loans - Risk Categories of Loans by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,828,441	$ 4,825,214
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	4,690,296	4,694,297
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	85,110	67,296
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	53,035	63,596
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	25
Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	417,565	443,568
Construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	406,010	428,044
Construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	11,262	10,429
Construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	293	5,095
Construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,162,417	2,132,066
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,080,415	2,063,589
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	57,732	41,429
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	24,270	27,048
Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,329,166	1,324,377
Residential real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,304,847	1,296,634
Residential real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	3,953	3,654
Residential real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	20,366	24,089
Residential real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial and financial
Financing Receivable, Recorded Investment [Line Items]
Loans	712,879	722,322
Commercial and financial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	696,837	707,663
Commercial and financial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	9,013	8,387
Commercial and financial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	7,029	6,247
Commercial and financial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	25
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	206,414	202,881
Consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	202,187	198,367
Consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	3,150	3,397
Consumer | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	1,077	1,117
Consumer | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0