Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 13,667,372	$ 12,990,779
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,659,622	7,458,401
Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,184,283	1,901,526
Originated | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,405,772	1,921,799
Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	349,395	281,724
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,007,750	5,532,378
Commercial loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,131,162	7,594,212
Commercial loan portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,763,613	7,167,397
Commercial loan portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	156,325	192,013
Commercial loan portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	206,427	233,479
Commercial loan portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,797	1,323
Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,360,161	3,217,300
Commercial loan portfolio | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,324,323	3,973,140
Commercial loan portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	446,678	403,772
Commercial loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,939,450	4,105,049
Commercial loan portfolio | Originated | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,792,613	3,934,033
Commercial loan portfolio | Originated | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	60,891	81,947
Commercial loan portfolio | Originated | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	81,317	87,999
Commercial loan portfolio | Originated | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,629	1,070
Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,184,283	1,901,526
Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,101,781	1,803,750
Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,051	44,809
Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	47,871	51,898
Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,580	1,069
Commercial loan portfolio | Originated | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,405,772	1,921,799
Commercial loan portfolio | Originated | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,341,493	1,849,315
Commercial loan portfolio | Originated | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,840	36,981
Commercial loan portfolio | Originated | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,390	35,502
Commercial loan portfolio | Originated | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,049	1
Commercial loan portfolio | Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	349,395	281,724
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	349,339	280,968
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	157
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	56	599
Commercial loan portfolio | Originated | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial loan portfolio | Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,191,712	3,489,163
Commercial loan portfolio | Acquired | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,971,000	3,233,364
Commercial loan portfolio | Acquired | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	95,434	110,066
Commercial loan portfolio | Acquired | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	125,110	145,480
Commercial loan portfolio | Acquired | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	168	253
Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,175,878	1,315,774
Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,100,238	1,218,848
Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	30,686	46,643
Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	44,951	50,283
Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	0
Commercial loan portfolio | Acquired | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,918,551	2,051,341
Commercial loan portfolio | Acquired | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,777,461	1,897,011
Commercial loan portfolio | Acquired | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	62,807	61,441
Commercial loan portfolio | Acquired | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	78,118	92,636
Commercial loan portfolio | Acquired | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	165	253
Commercial loan portfolio | Acquired | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	97,283	122,048
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	93,301	117,505
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,941	1,982
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,041	2,561
Commercial loan portfolio | Acquired | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0