Loans (Summary of Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of loans under portfolio
Loans	$ 14,155,267	$ 12,990,779
Deferred costs	26,100	14,800
Commercial
Summary of loans under portfolio
Loans		3,217,300
Commercial real estate
Summary of loans under portfolio
Loans		3,973,140
Real estate construction and land development
Summary of loans under portfolio
Loans		403,772
Residential mortgage
Summary of loans under portfolio
Loans		3,086,474
Consumer installment
Summary of loans under portfolio
Loans		1,433,884
Home equity
Summary of loans under portfolio
Loans		876,209
Commercial Originated Portfolio
Summary of loans under portfolio
Loans	5,657,186	4,105,049
Commercial Originated Portfolio | Commercial
Summary of loans under portfolio
Loans	2,407,606	1,901,526
Commercial Originated Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	2,751,425	1,921,799
Commercial Originated Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	498,155	281,724
Consumer Originated Portfolio
Summary of loans under portfolio
Loans	4,090,243	3,353,352
Consumer Originated Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,967,857	1,475,342
Consumer Originated Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,510,540	1,282,588
Consumer Originated Portfolio | Home equity
Summary of loans under portfolio
Loans	611,846	595,422
Originated Portfolio
Summary of loans under portfolio
Loans	9,747,429	7,458,401
Originated Portfolio | Commercial
Summary of loans under portfolio
Loans	2,407,606	1,901,526
Originated Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	2,751,425	1,921,799
Originated Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	498,155	281,724
Originated Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,967,857	1,475,342
Originated Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,510,540	1,282,588
Originated Portfolio | Home equity
Summary of loans under portfolio
Loans	611,846	595,422
Commercial Acquired Portfolio
Summary of loans under portfolio
Loans	2,803,341	3,489,163
Commercial Acquired Portfolio | Commercial
Summary of loans under portfolio
Loans	978,036	1,315,774
Commercial Acquired Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	1,749,245	2,051,341
Commercial Acquired Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	76,060	122,048
Consumer Acquired Portfolio
Summary of loans under portfolio
Loans	1,604,497	2,043,215
Consumer Acquired Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	1,284,630	1,611,132
Consumer Acquired Portfolio | Consumer installment
Summary of loans under portfolio
Loans	102,468	151,296
Consumer Acquired Portfolio | Home equity
Summary of loans under portfolio
Loans	217,399	280,787
Acquired Portfolio
Summary of loans under portfolio
Loans	4,407,838	5,532,378
Commercial Loan Portfolio
Summary of loans under portfolio
Loans	8,460,527	7,594,212
Commercial Loan Portfolio | Commercial
Summary of loans under portfolio
Loans	3,385,642
Commercial Loan Portfolio | Commercial real estate
Summary of loans under portfolio
Loans	4,500,670
Commercial Loan Portfolio | Real estate construction and land development
Summary of loans under portfolio
Loans	574,215
Consumer Loan Portfolio
Summary of loans under portfolio
Loans	5,694,740	5,396,567
Consumer Loan Portfolio | Residential mortgage
Summary of loans under portfolio
Loans	3,252,487	3,086,474
Consumer Loan Portfolio | Consumer installment
Summary of loans under portfolio
Loans	1,613,008	1,433,884
Consumer Loan Portfolio | Home equity
Summary of loans under portfolio
Loans	$ 829,245	$ 876,209