Loans - Aging Status of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule representing the aging status of the recorded investment in loans by classes
Total loans	$ 14,796,252	$ 14,155,267
90 days or more past due and still accruing	1,192	1,377
Commercial
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	632	0
Total commercial real estate
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	47	13
Real estate construction and land development
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	38	0
Home equity
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	475	1,364
Originated Portfolio
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	111,617	58,857
Current	11,033,825	9,688,572
Total loans	11,145,442	9,747,429
90 days or more past due and still accruing	1,192	1,377
Originated Portfolio | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	33,475	31,724
Originated Portfolio | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	29,965	8,486
Originated Portfolio | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	48,177	18,647
Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	30,905	27,166
Current	2,920,548	2,380,440
Total loans	2,951,453	2,407,606
90 days or more past due and still accruing	632	0
Originated Portfolio | Commercial | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	9,280	13,906
Originated Portfolio | Commercial | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	8,770	3,766
Originated Portfolio | Commercial | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	12,855	9,494
Originated Portfolio | Total commercial real estate
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	27,895	16,815
Current	3,228,311	2,734,610
Total loans	3,256,206	2,751,425
90 days or more past due and still accruing	47	13
Originated Portfolio | Total commercial real estate | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	10,322	9,380
Originated Portfolio | Total commercial real estate | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	4,601	1,562
Originated Portfolio | Total commercial real estate | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	12,972	5,873
Originated Portfolio | Real estate construction and land development
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	29,759	0
Current	524,942	498,155
Total loans	554,701	498,155
90 days or more past due and still accruing	38	0
Originated Portfolio | Real estate construction and land development | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,244	0
Originated Portfolio | Real estate construction and land development | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	13,238	0
Originated Portfolio | Real estate construction and land development | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	15,277	0
Originated Portfolio | Residential mortgage
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	10,217	5,068
Current	2,275,394	1,962,789
Total loans	2,285,611	1,967,857
90 days or more past due and still accruing	0	0
Originated Portfolio | Residential mortgage | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,889	2,795
Originated Portfolio | Residential mortgage | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,576	1,415
Originated Portfolio | Residential mortgage | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	4,752	858
Originated Portfolio | Consumer installment
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	4,829	3,992
Current	1,478,711	1,506,548
Total loans	1,483,540	1,510,540
90 days or more past due and still accruing	0	0
Originated Portfolio | Consumer installment | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,555	3,324
Originated Portfolio | Consumer installment | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	657	442
Originated Portfolio | Consumer installment | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	617	226
Originated Portfolio | Home equity
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	8,012	5,816
Current	605,919	606,030
Total loans	613,931	611,846
90 days or more past due and still accruing	475	1,364
Originated Portfolio | Home equity | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	5,185	2,319
Originated Portfolio | Home equity | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,123	1,301
Originated Portfolio | Home equity | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,704	2,196
Owner-occupied | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	47	0
Owner-occupied | Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	18,950	13,977
Current	1,315,638	1,171,637
Total loans	1,334,588	1,185,614
90 days or more past due and still accruing	47	0
Owner-occupied | Originated Portfolio | Commercial | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	8,052	7,644
Owner-occupied | Originated Portfolio | Commercial | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	2,440	1,306
Owner-occupied | Originated Portfolio | Commercial | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	8,458	5,027
Non-owner occupied | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	0	13
Non-owner occupied | Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	4,809	2,574
Current	1,870,346	1,516,213
Total loans	1,875,155	1,518,787
90 days or more past due and still accruing	0	13
Non-owner occupied | Originated Portfolio | Commercial | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,993	1,653
Non-owner occupied | Originated Portfolio | Commercial | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	762	228
Non-owner occupied | Originated Portfolio | Commercial | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	2,054	693
Vacant land | Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	4,136	264
Current	42,327	46,760
Total loans	46,463	47,024
90 days or more past due and still accruing	0	0
Vacant land | Originated Portfolio | Commercial | 30-59 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	277	83
Vacant land | Originated Portfolio | Commercial | 60-89 days past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	1,399	28
Vacant land | Originated Portfolio | Commercial | 90 days or more past due
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	$ 2,460	$ 153