Loans - Summary of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Summary of loans under portfolio
Total loans	$ 14,218,747	$ 14,155,267
Deferred income	23,900	26,100
Commercial loan portfolio
Summary of loans under portfolio
Total loans	8,575,441	8,460,527
Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	3,427,285	3,385,642
Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	4,588,376	4,500,670
Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	559,780	574,215
Consumer loan portfolio
Summary of loans under portfolio
Total loans	5,643,306	5,694,740
Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	3,264,620	3,252,487
Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,572,240	1,613,008
Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	806,446	829,245
Originated
Summary of loans under portfolio
Total loans	10,012,516	9,747,429
Originated | Commercial
Summary of loans under portfolio
Total loans	2,486,533	2,407,606
Originated | Total commercial real estate
Summary of loans under portfolio
Total loans	2,918,803	2,751,425
Originated | Real estate construction and land development
Summary of loans under portfolio
Total loans	485,474	498,155
Originated | Residential mortgage
Summary of loans under portfolio
Total loans	2,039,349	1,967,857
Originated | Consumer installment
Summary of loans under portfolio
Total loans	1,478,673	1,510,540
Originated | Home equity
Summary of loans under portfolio
Total loans	603,684	611,846
Originated | Commercial loan portfolio
Summary of loans under portfolio
Total loans	5,890,810	5,657,186
Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,486,533	2,407,606
Originated | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	2,918,803	2,751,425
Originated | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	485,474	498,155
Originated | Consumer loan portfolio
Summary of loans under portfolio
Total loans	4,121,706	4,090,243
Originated | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	2,039,349	1,967,857
Originated | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,478,673	1,510,540
Originated | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	603,684	611,846
Acquired
Summary of loans under portfolio
Total loans	4,206,231	4,407,838
Acquired | Commercial loan portfolio
Summary of loans under portfolio
Total loans	2,684,631	2,803,341
Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	940,752	978,036
Acquired | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	1,669,573	1,749,245
Acquired | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	74,306	76,060
Acquired | Consumer loan portfolio
Summary of loans under portfolio
Total loans	1,521,600	1,604,497
Acquired | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,225,271	1,284,630
Acquired | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	93,567	102,468
Acquired | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	202,762	217,399
Owner-occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,832,824	1,813,562
Owner-occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,185,797	1,185,614
Owner-occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,185,797	1,185,614
Owner-occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	647,027	627,948
Non-owner occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,680,801	2,606,761
Non-owner occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,689,022	1,518,787
Non-owner occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,689,022	1,518,787
Non-owner occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	991,779	1,087,974
Vacant land | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	74,751	80,347
Vacant land | Originated | Commercial
Summary of loans under portfolio
Total loans	43,984	47,024
Vacant land | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	43,984	47,024
Vacant land | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	$ 30,767	$ 33,323