Loans - Summary of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Summary of loans under portfolio
Total loans	$ 14,796,252	$ 14,155,267
Deferred income	19,000	26,100
Commercial loan portfolio
Summary of loans under portfolio
Total loans	9,053,690	8,460,527
Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	3,719,922	3,385,642
Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	4,711,621	4,500,670
Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	622,147	574,215
Consumer loan portfolio
Summary of loans under portfolio
Total loans	5,742,562	5,694,740
Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	3,391,987	3,252,487
Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,560,265	1,613,008
Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	790,310	829,245
Originated
Summary of loans under portfolio
Total loans	11,145,442	9,747,429
Originated | Commercial
Summary of loans under portfolio
Total loans	2,951,453	2,407,606
Originated | Total commercial real estate
Summary of loans under portfolio
Total loans	3,256,206	2,751,425
Originated | Real estate construction and land development
Summary of loans under portfolio
Total loans	554,701	498,155
Originated | Residential mortgage
Summary of loans under portfolio
Total loans	2,285,611	1,967,857
Originated | Consumer installment
Summary of loans under portfolio
Total loans	1,483,540	1,510,540
Originated | Home equity
Summary of loans under portfolio
Total loans	613,931	611,846
Originated | Commercial loan portfolio
Summary of loans under portfolio
Total loans	6,762,360	5,657,186
Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,951,453	2,407,606
Originated | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	3,256,206	2,751,425
Originated | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	554,701	498,155
Originated | Consumer loan portfolio
Summary of loans under portfolio
Total loans	4,383,082	4,090,243
Originated | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	2,285,611	1,967,857
Originated | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,483,540	1,510,540
Originated | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	613,931	611,846
Acquired
Summary of loans under portfolio
Total loans	3,650,810	4,407,838
Acquired | Commercial loan portfolio
Summary of loans under portfolio
Total loans	2,291,330	2,803,341
Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	768,469	978,036
Acquired | Commercial loan portfolio | Total commercial real estate
Summary of loans under portfolio
Total loans	1,455,415	1,749,245
Acquired | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	67,446	76,060
Acquired | Consumer loan portfolio
Summary of loans under portfolio
Total loans	1,359,480	1,604,497
Acquired | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,106,376	1,284,630
Acquired | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	76,725	102,468
Acquired | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	176,379	217,399
Owner-occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,897,934	1,813,562
Owner-occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,334,588	1,185,614
Owner-occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,334,588	1,185,614
Owner-occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	563,346	627,948
Non-owner occupied | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,739,700	2,606,761
Non-owner occupied | Originated | Commercial
Summary of loans under portfolio
Total loans	1,875,155	1,518,787
Non-owner occupied | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,875,155	1,518,787
Non-owner occupied | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	864,545	1,087,974
Vacant land | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	73,987	80,347
Vacant land | Originated | Commercial
Summary of loans under portfolio
Total loans	46,463	47,024
Vacant land | Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	46,463	47,024
Vacant land | Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	$ 27,524	$ 33,323