Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 15,861,903	$ 15,269,779
Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	12,871,110	11,844,756
Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,752,528	3,287,087
Originated | Total commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,622,488	3,520,157
Originated | Real estate construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	671,773	566,726
Acquired
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,990,793	3,425,023
Commercial loan portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	9,895,855	9,511,867
Commercial loan portfolio | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	9,354,289	8,998,284
Commercial loan portfolio | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	282,192	283,400
Commercial loan portfolio | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	250,024	225,924
Commercial loan portfolio | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	9,350	4,259
Commercial loan portfolio | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,347,885	4,002,568
Commercial loan portfolio | Total commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,847,200	4,912,087
Commercial loan portfolio | Real estate construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	700,770	597,212
Commercial loan portfolio | Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	8,046,789	7,373,970
Commercial loan portfolio | Originated | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	7,689,269	7,045,203
Commercial loan portfolio | Originated | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	158,331	164,802
Commercial loan portfolio | Originated | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	192,055	159,733
Commercial loan portfolio | Originated | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	7,134	4,232
Commercial loan portfolio | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,752,528	3,287,087
Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,513,993	3,118,894
Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	123,194	87,222
Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	108,373	77,036
Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	6,968	3,935
Commercial loan portfolio | Originated | Total commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,622,488	3,520,157
Commercial loan portfolio | Originated | Total commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,511,154	3,369,269
Commercial loan portfolio | Originated | Total commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	31,525	71,472
Commercial loan portfolio | Originated | Total commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	79,643	79,119
Commercial loan portfolio | Originated | Total commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	166	297
Commercial loan portfolio | Originated | Real estate construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	671,773	566,726
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	664,122	557,040
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,612	6,108
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,039	3,578
Commercial loan portfolio | Originated | Real estate construction and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial loan portfolio | Acquired
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,849,066	2,137,897
Commercial loan portfolio | Acquired | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,665,020	1,953,081
Commercial loan portfolio | Acquired | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	123,861	118,598
Commercial loan portfolio | Acquired | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	57,969	66,191
Commercial loan portfolio | Acquired | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,216	27
Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	595,357	715,481
Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	505,823	655,883
Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	62,253	36,809
Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	25,512	22,773
Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,769	16
Commercial loan portfolio | Acquired | Total commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,224,712	1,391,930
Commercial loan portfolio | Acquired | Total commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,130,482	1,267,950
Commercial loan portfolio | Acquired | Total commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	61,566	81,692
Commercial loan portfolio | Acquired | Total commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	32,217	42,277
Commercial loan portfolio | Acquired | Total commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	447	11
Commercial loan portfolio | Acquired | Real estate construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	28,997	30,486
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	28,715	29,248
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	42	97
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	240	1,141
Commercial loan portfolio | Acquired | Real estate construction and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Owner-occupied | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,528,802	1,513,532
Owner-occupied | Commercial loan portfolio | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,024,561	2,059,557
Owner-occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,528,802	1,513,532
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,452,031	1,430,948
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	25,913	32,056
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	50,697	50,286
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	161	242
Owner-occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	495,759	546,025
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	462,266	500,072
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	18,226	28,909
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	14,835	17,033
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	432	11
Non-owner occupied | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,056,531	1,966,330
Non-owner occupied | Commercial loan portfolio | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,772,677	2,785,020
Non-owner occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,056,531	1,966,330
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,023,577	1,901,822
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	5,516	39,416
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	27,433	25,092
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	5	0
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	716,146	818,690
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	655,602	740,900
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	43,147	52,546
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	17,382	25,244
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	15	0
Vacant land | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	37,155	40,295
Vacant land | Commercial loan portfolio | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	49,962	67,510
Vacant land | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	37,155	40,295
Vacant land | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	35,546	36,499
Vacant land | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	96	0
Vacant land | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,513	3,741
Vacant land | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	55
Vacant land | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	12,807	27,215
Vacant land | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	12,614	26,978
Vacant land | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	193	237
Vacant land | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Vacant land | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 0	$ 0