Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,796,252	$ 14,155,267
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,145,442	9,747,429
Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,951,453	2,407,606
Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,256,206	2,751,425
Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	554,701	498,155
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,650,810	4,407,838
Commercial loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,053,690	8,460,527
Commercial loan portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,629,934	8,038,463
Commercial loan portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	203,735	204,706
Commercial loan portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	219,988	216,353
Commercial loan portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	33	1,005
Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,719,922	3,385,642
Commercial loan portfolio | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,711,621	4,500,670
Commercial loan portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	622,147	574,215
Commercial loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,762,360	5,657,186
Commercial loan portfolio | Originated | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,518,563	5,488,571
Commercial loan portfolio | Originated | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	105,670	66,100
Commercial loan portfolio | Originated | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	138,105	102,515
Commercial loan portfolio | Originated | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	22	0
Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,951,453	2,407,606
Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,840,100	2,316,464
Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	54,258	41,059
Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,095	50,083
Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial loan portfolio | Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,256,206	2,751,425
Commercial loan portfolio | Originated | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,160,902	2,677,579
Commercial loan portfolio | Originated | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,312	24,204
Commercial loan portfolio | Originated | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	48,970	49,642
Commercial loan portfolio | Originated | Total commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	22	0
Commercial loan portfolio | Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	554,701	498,155
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	517,561	494,528
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,100	837
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,040	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	2,291,330	2,803,341
Commercial loan portfolio | Acquired | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,111,371	2,549,892
Commercial loan portfolio | Acquired | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	98,065	138,606
Commercial loan portfolio | Acquired | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	81,883	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	768,469	978,036
Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	707,054	873,861
Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,227	68,418
Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	25,188	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	1,455,415	1,749,245
Commercial loan portfolio | Acquired | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,338,023	1,603,685
Commercial loan portfolio | Acquired | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	61,700	67,970
Commercial loan portfolio | Acquired | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	55,681	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	67,446	76,060
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	66,294	72,346
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	138	2,218
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,014	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	1,334,588	1,185,614
Owner-occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,897,934	1,813,562
Owner-occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,334,588	1,185,614
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,265,111	1,133,609
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,290	19,438
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,168	32,567
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	19	0
Owner-occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	563,346	627,948
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	505,246	580,127
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,840	23,998
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	28,249	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	1,875,155	1,518,787
Non-owner occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,739,700	2,606,761
Non-owner occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,875,155	1,518,787
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,854,887	1,504,195
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,542	4,728
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,726	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	864,545	1,087,974
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	805,466	995,709
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,647	43,645
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,432	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	46,463	47,024
Vacant land | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	73,987	80,347
Vacant land | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,463	47,024
Vacant land | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	40,904	39,775
Vacant land | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	480	38
Vacant land | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,076	7,211
Vacant land | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	0
Vacant land | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,524	33,323
Vacant land | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,311	27,849
Vacant land | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	213	327
Vacant land | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	5,147
Vacant land | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0