Loans - Summary of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Summary of loans under portfolio
Total loans	$ 14,579,693	$ 14,155,267
Deferred income	22,600	26,100
Commercial loan portfolio
Summary of loans under portfolio
Total loans	8,866,695	8,460,527
Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	3,576,438	3,385,642
Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	4,671,272	4,500,670
Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	618,985	574,215
Consumer loan portfolio
Summary of loans under portfolio
Total loans	5,712,998	5,694,740
Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	3,325,277	3,252,487
Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,587,327	1,613,008
Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	800,394	829,245
Originated
Summary of loans under portfolio
Total loans	10,696,533	9,747,429
Originated | Commercial
Summary of loans under portfolio
Total loans	2,753,604	2,407,606
Originated | Total commercial real estate
Summary of loans under portfolio
Total loans	3,118,329	2,751,425
Originated | Real estate construction and land development
Summary of loans under portfolio
Total loans	550,447	498,155
Originated | Residential mortgage
Summary of loans under portfolio
Total loans	2,162,225	1,967,857
Originated | Consumer installment
Summary of loans under portfolio
Total loans	1,501,900	1,510,540
Originated | Home equity
Summary of loans under portfolio
Total loans	610,028	611,846
Originated | Commercial loan portfolio
Summary of loans under portfolio
Total loans	6,422,380	5,657,186
Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,753,604	2,407,606
Originated | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	3,118,329	2,751,425
Originated | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	550,447	498,155
Originated | Consumer loan portfolio
Summary of loans under portfolio
Total loans	4,274,153	4,090,243
Originated | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	2,162,225	1,967,857
Originated | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,501,900	1,510,540
Originated | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	610,028	611,846
Acquired
Summary of loans under portfolio
Total loans	3,883,160	4,407,838
Acquired | Commercial loan portfolio
Summary of loans under portfolio
Total loans	2,444,315	2,803,341
Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	822,834	978,036
Acquired | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	1,552,943	1,749,245
Acquired | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	68,538	76,060
Acquired | Consumer loan portfolio
Summary of loans under portfolio
Total loans	1,438,845	1,604,497
Acquired | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,163,052	1,284,630
Acquired | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	85,427	102,468
Acquired | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	190,366	217,399
Owner-occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,863,563	1,813,562
Owner-occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,252,383	1,185,614
Owner-occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,252,383	1,185,614
Owner-occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	611,180	627,948
Non-owner occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,728,103	2,606,761
Non-owner occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,819,535	1,518,787
Non-owner occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,819,535	1,518,787
Non-owner occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	908,568	1,087,974
Vacant land | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	79,606	80,347
Vacant land | Originated | Commercial
Summary of loans under portfolio
Total loans	46,411	47,024
Vacant land | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	46,411	47,024
Vacant land | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	$ 33,195	$ 33,323