Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,579,693	$ 14,155,267
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,696,533	9,747,429
Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,753,604	2,407,606
Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,118,329	2,751,425
Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	550,447	498,155
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,883,160	4,407,838
Commercial loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,866,695	8,460,527
Commercial loan portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,427,929	8,038,463
Commercial loan portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	191,245	204,706
Commercial loan portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	246,773	216,353
Commercial loan portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	748	1,005
Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,576,438	3,385,642
Commercial loan portfolio | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,671,272	4,500,670
Commercial loan portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	618,985	574,215
Commercial loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,422,380	5,657,186
Commercial loan portfolio | Originated | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,199,010	5,488,571
Commercial loan portfolio | Originated | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	83,106	66,100
Commercial loan portfolio | Originated | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	139,527	102,515
Commercial loan portfolio | Originated | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	737	0
Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,753,604	2,407,606
Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,654,995	2,316,464
Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,619	41,059
Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,300	50,083
Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	690	0
Commercial loan portfolio | Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,118,329	2,751,425
Commercial loan portfolio | Originated | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,027,447	2,677,579
Commercial loan portfolio | Originated | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	38,314	24,204
Commercial loan portfolio | Originated | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	52,521	49,642
Commercial loan portfolio | Originated | Total commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	47	0
Commercial loan portfolio | Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	550,447	498,155
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	516,568	494,528
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,173	837
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,706	2,790
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	2,444,315	2,803,341
Commercial loan portfolio | Acquired | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,228,919	2,549,892
Commercial loan portfolio | Acquired | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	108,139	138,606
Commercial loan portfolio | Acquired | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	107,246	113,838
Commercial loan portfolio | Acquired | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	1,005
Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	822,834	978,036
Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	748,719	873,861
Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	43,301	68,418
Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	30,814	35,539
Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	218
Commercial loan portfolio | Acquired | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,552,943	1,749,245
Commercial loan portfolio | Acquired | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,412,989	1,603,685
Commercial loan portfolio | Acquired | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,468	67,970
Commercial loan portfolio | Acquired | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	75,475	76,803
Commercial loan portfolio | Acquired | Total commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	787
Commercial loan portfolio | Acquired | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	68,538	76,060
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	67,211	72,346
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	370	2,218
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	957	1,496
Commercial loan portfolio | Acquired | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Owner-occupied | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,252,383	1,185,614
Owner-occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,863,563	1,813,562
Owner-occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,252,383	1,185,614
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,186,100	1,133,609
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	25,247	19,438
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,990	32,567
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	46	0
Owner-occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	611,180	627,948
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	548,079	580,127
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,767	23,998
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,323	23,036
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	787
Non-owner occupied | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,819,535	1,518,787
Non-owner occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,728,103	2,606,761
Non-owner occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,819,535	1,518,787
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,800,859	1,504,195
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,891	4,728
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,785	9,864
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	908,568	1,087,974
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	836,864	995,709
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,391	43,645
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,313	48,620
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Vacant land | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,411	47,024
Vacant land | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	79,606	80,347
Vacant land | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,411	47,024
Vacant land | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,488	39,775
Vacant land | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	176	38
Vacant land | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,746	7,211
Vacant land | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	1	0
Vacant land | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,195	33,323
Vacant land | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	28,046	27,849
Vacant land | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	310	327
Vacant land | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,839	5,147
Vacant land | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0