Loans - Aging Status of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule representing the aging status of the recorded investment in loans by classes
Total loans	$ 14,218,747	$ 14,155,267
90 days or more past due and still accruing	1,235	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	322	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	0	13
Home equity
Schedule representing the aging status of the recorded investment in loans by classes
90 days or more past due and still accruing	913	1,364
Originated Portfolio
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	72,236	58,857
Current	9,940,280	9,688,572
Total loans	10,012,516	9,747,429
90 days or more past due and still accruing	1,235	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	33,510	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	12,520	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	26,206	18,647
Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	26,890	27,166
Current	2,459,643	2,380,440
Total loans	2,486,533	2,407,606
90 days or more past due and still accruing	322	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	8,689	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	6,079	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	12,122	9,494
Originated Portfolio | Total commercial real estate
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	29,020	16,815
Current	2,889,783	2,734,610
Total loans	2,918,803	2,751,425
90 days or more past due and still accruing	0	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	15,253	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	4,265	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	9,502	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	100	0
Current	485,374	498,155
Total loans	485,474	498,155
90 days or more past due and still accruing	0	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	100	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	0	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	0	0
Originated Portfolio | Residential mortgage
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	5,542	5,068
Current	2,033,807	1,962,789
Total loans	2,039,349	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	3,020	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	246	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	2,276	858
Originated Portfolio | Consumer installment
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	3,644	3,992
Current	1,475,029	1,506,548
Total loans	1,478,673	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	2,817	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	570	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	257	226
Originated Portfolio | Home equity
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	7,040	5,816
Current	596,644	606,030
Total loans	603,684	611,846
90 days or more past due and still accruing	913	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	3,631	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	1,360	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	2,049	2,196
Owner-occupied | Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	22,591	13,977
Current	1,163,206	1,171,637
Total loans	1,185,797	1,185,614
90 days or more past due and still accruing	0	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	10,829	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	3,368	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	8,394	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	5,574	2,574
Current	1,683,448	1,516,213
Total loans	1,689,022	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	3,749	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	897	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	928	693
Vacant land | Originated Portfolio | Commercial
Schedule representing the aging status of the recorded investment in loans by classes
Total past due	855	264
Current	43,129	46,760
Total loans	43,984	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	675	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	0	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	$ 180	$ 153