Loans - Contractual Aging of Recorded Investment in Past Due Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 3,869,778	$ 3,788,998
Nonaccrual	19,339	19,524
Total Financing Receivables	3,897,125	3,817,377
Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	7,119	8,082
Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	660	773
Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	229	0
Portfolio Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,044,590	2,903,109
Nonaccrual	12,628	12,569
Total Financing Receivables	3,063,618	2,922,609
Portfolio Loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,194,839	1,165,738
Nonaccrual	1,017	1,690
Total Financing Receivables	1,197,152	1,170,618
Portfolio Loans [Member] | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	530,801	507,501
Nonaccrual	1,969	2,127
Total Financing Receivables	536,321	512,430
Portfolio Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	187,818	178,676
Nonaccrual	85	98
Total Financing Receivables	188,195	178,826
Portfolio Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	5,842	6,245
Portfolio Loans [Member] | Accruing 30-59 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,296	2,605
Portfolio Loans [Member] | Accruing 30-59 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	3,149	2,776
Portfolio Loans [Member] | Accruing 30-59 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	218	52
Portfolio Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	329	686
Portfolio Loans [Member] | Accruing 60-89 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	585
Portfolio Loans [Member] | Accruing 60-89 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	173	26
Portfolio Loans [Member] | Accruing 60-89 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	74	0
Portfolio Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	229	0
Portfolio Loans [Member] | Accruing Greater Than 90 Days | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Portfolio Loans [Member] | Accruing Greater Than 90 Days | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	229	0
Portfolio Loans [Member] | Accruing Greater Than 90 Days | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	813,244	874,028
Nonaccrual	4,962	2,041
Total Financing Receivables	819,814	877,351
Purchased Unimpaired Loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	436,589	457,899
Nonaccrual	708	720
Total Financing Receivables	438,232	459,598
Purchased Unimpaired Loans [Member] | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	79,400	92,315
Financing Receivable, Recorded Investment, Past Due	2
Nonaccrual	160	321
Total Financing Receivables	79,562	92,690
Purchased Unimpaired Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,588	10,610
Nonaccrual	0	0
Total Financing Receivables	7,593	10,610
Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,277	1,195
Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	609	979
Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due		54
Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	331	87
Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	326	0
Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	5	0
Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	11,944	11,861
Nonaccrual	1,749	4,914
Total Financing Receivables	13,693	17,417
Purchased Credit Impaired Loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,427	9,352
Nonaccrual	428	424
Total Financing Receivables	9,855	9,776
Purchased Credit Impaired Loans [Member] | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	819	844
Financing Receivable, Recorded Investment, Past Due	0
Nonaccrual	0	50
Total Financing Receivables	819	894
Purchased Credit Impaired Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	0	0
Nonaccrual	0	0
Total Financing Receivables	0	0
Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	642
Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due		0
Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days | Commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days | Commercial And Financials [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Portfolio Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	253,189	215,077
Nonaccrual	227	238
Total Financing Receivables	253,416	215,315
Construction and land development [Member] | Portfolio Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Portfolio Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Portfolio Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Purchased Unimpaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	119,539	126,655
Nonaccrual	0	0
Total Financing Receivables	119,678	126,689
Construction and land development [Member] | Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	139	34
Construction and land development [Member] | Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,150	1,121
Nonaccrual	0	0
Total Financing Receivables	1,150	1,121
Construction and land development [Member] | Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Construction and land development [Member] | Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Financing Receivables	1,065,152	1,038,810
Residential real estate [Member] | Portfolio Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	877,943	836,117
Nonaccrual	9,330	8,416
Total Financing Receivables	888,534	845,420
Residential real estate [Member] | Portfolio Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,179	812
Residential real estate [Member] | Portfolio Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	82	75
Residential real estate [Member] | Portfolio Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Residential real estate [Member] | Purchased Unimpaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	170,128	186,549
Nonaccrual	4,094	1,000
Total Financing Receivables	174,749	187,764
Residential real estate [Member] | Purchased Unimpaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	527	128
Residential real estate [Member] | Purchased Unimpaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	87
Residential real estate [Member] | Purchased Unimpaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Residential real estate [Member] | Purchased Credit Impaired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	548	544
Nonaccrual	1,321	4,440
Total Financing Receivables	1,869	5,626
Residential real estate [Member] | Purchased Credit Impaired Loans [Member] | Accruing 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	642
Residential real estate [Member] | Purchased Credit Impaired Loans [Member] | Accruing 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Residential real estate [Member] | Purchased Credit Impaired Loans [Member] | Accruing Greater Than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 0	$ 0