Loans - Summary of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of loans under portfolio
Total loans	$ 13,833,368	$ 12,990,779
Deferred income	25,600	14,800
Commercial loan portfolio
Summary of loans under portfolio
Total loans	8,137,356	7,594,212
Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	3,319,965	3,217,300
Commercial loan portfolio | Commercial real estate
Summary of loans under portfolio
Total loans	4,315,978	3,973,140
Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	501,413	403,772
Consumer loan portfolio
Summary of loans under portfolio
Total loans	5,696,012	5,396,567
Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	3,221,307	3,086,474
Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,615,983	1,433,884
Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	858,722	876,209
Originated
Summary of loans under portfolio
Total loans	9,156,096	7,458,401
Originated | Commercial
Summary of loans under portfolio
Total loans	2,255,444	1,901,526
Originated | Commercial real estate
Summary of loans under portfolio
Total loans	2,472,224	1,921,799
Originated | Real estate construction and land development
Summary of loans under portfolio
Total loans	421,764	281,724
Originated | Residential mortgage
Summary of loans under portfolio
Total loans	1,881,285	1,475,342
Originated | Consumer installment
Summary of loans under portfolio
Total loans	1,502,814	1,282,588
Originated | Home equity
Summary of loans under portfolio
Total loans	622,565	595,422
Originated | Commercial loan portfolio
Summary of loans under portfolio
Total loans	5,149,432	4,105,049
Originated | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	2,255,444	1,901,526
Originated | Commercial loan portfolio | Commercial real estate
Summary of loans under portfolio
Total loans	2,472,224	1,921,799
Originated | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	421,764	281,724
Originated | Consumer loan portfolio
Summary of loans under portfolio
Total loans	4,006,664	3,353,352
Originated | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,881,285	1,475,342
Originated | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	1,502,814	1,282,588
Originated | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	622,565	595,422
Acquired
Summary of loans under portfolio
Total loans	4,677,272	5,532,378
Acquired | Commercial loan portfolio
Summary of loans under portfolio
Total loans	2,987,924	3,489,163
Acquired | Commercial loan portfolio | Commercial
Summary of loans under portfolio
Total loans	1,064,521	1,315,774
Acquired | Commercial loan portfolio | Commercial real estate
Summary of loans under portfolio
Total loans	1,843,754	2,051,341
Acquired | Commercial loan portfolio | Real estate construction and land development
Summary of loans under portfolio
Total loans	79,649	122,048
Acquired | Consumer loan portfolio
Summary of loans under portfolio
Total loans	1,689,348	2,043,215
Acquired | Consumer loan portfolio | Residential mortgage
Summary of loans under portfolio
Total loans	1,340,022	1,611,132
Acquired | Consumer loan portfolio | Consumer installment
Summary of loans under portfolio
Total loans	113,169	151,296
Acquired | Consumer loan portfolio | Home equity
Summary of loans under portfolio
Total loans	$ 236,157	$ 280,787