Loans - Summary of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Summary of loans under portfolio
Total loans	$ 15,324,048	$ 15,269,779
Deferred income	22,200	19,700
Commercial loan portfolio
Summary of loans under portfolio
Total loans	9,511,831	9,511,867
Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	4,054,072	4,002,568
Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	4,835,169	4,912,087
Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	622,590	597,212
Consumer loan portfolio
Summary of loans under portfolio
Total loans	5,812,217	5,757,912
Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	3,549,617	3,458,666
Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,504,441	1,521,074
Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	758,159	778,172
Originated
Summary of loans under portfolio
Total loans	12,142,274	11,844,756
Originated | Commercial
Summary of loans under portfolio
Total loans	3,428,432	3,287,087
Originated | Total commercial real estate
Summary of loans under portfolio
Total loans	3,535,273	3,520,157
Originated | Real estate construction and land development
Summary of loans under portfolio
Total loans	592,289	566,726
Originated | Residential mortgage
Summary of loans under portfolio
Total loans	2,542,943	2,407,305
Originated | Consumer installment
Summary of loans under portfolio
Total loans	1,440,193	1,451,352
Originated | Home equity
Summary of loans under portfolio
Total loans	603,144	612,129
Originated | Commercial loan portfolio
Summary of loans under portfolio
Total loans	7,555,994	7,373,970
Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	3,428,432	3,287,087
Originated | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	3,535,273	3,520,157
Originated | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	592,289	566,726
Originated | Consumer loan portfolio
Summary of loans under portfolio
Total loans	4,586,280	4,470,786
Originated | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	2,542,943	2,407,305
Originated | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,440,193	1,451,352
Originated | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	603,144	612,129
Acquired
Summary of loans under portfolio
Total loans	3,181,774	3,425,023
Acquired | Commercial loan portfolio
Summary of loans under portfolio
Total loans	1,955,837	2,137,897
Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	625,640	715,481
Acquired | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	1,299,896	1,391,930
Acquired | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	30,301	30,486
Acquired | Consumer loan portfolio
Summary of loans under portfolio
Total loans	1,225,937	1,287,126
Acquired | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,006,674	1,051,361
Acquired | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	64,248	69,722
Acquired | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	155,015	166,043
Owner-occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,050,430	2,059,557
Owner-occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,536,956	1,513,532
Owner-occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,536,956	1,513,532
Owner-occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	513,474	546,025
Non-owner occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,736,320	2,785,020
Non-owner occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,961,863	1,966,330
Non-owner occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,961,863	1,966,330
Non-owner occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	774,457	818,690
Vacant land | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	48,419	67,510
Vacant land | Originated | Commercial
Summary of loans under portfolio
Total loans	36,454	40,295
Vacant land | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	36,454	40,295
Vacant land | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	$ 11,965	$ 27,215