Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 15,324,048	$ 15,269,779
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,142,274	11,844,756
Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,428,432	3,287,087
Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,535,273	3,520,157
Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	592,289	566,726
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,181,774	3,425,023
Commercial loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,511,831	9,511,867
Commercial loan portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,000,511	8,998,284
Commercial loan portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	277,570	283,400
Commercial loan portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	224,940	225,924
Commercial loan portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,810	4,259
Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,054,072	4,002,568
Commercial loan portfolio | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,835,169	4,912,087
Commercial loan portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	622,590	597,212
Commercial loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,555,994	7,373,970
Commercial loan portfolio | Originated | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,208,328	7,045,203
Commercial loan portfolio | Originated | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	171,715	164,802
Commercial loan portfolio | Originated | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	167,163	159,733
Commercial loan portfolio | Originated | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,788	4,232
Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,428,432	3,287,087
Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,242,753	3,118,894
Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	87,939	87,222
Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	89,169	77,036
Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,571	3,935
Commercial loan portfolio | Originated | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,535,273	3,520,157
Commercial loan portfolio | Originated | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,387,882	3,369,269
Commercial loan portfolio | Originated | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	72,843	71,472
Commercial loan portfolio | Originated | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	74,331	79,119
Commercial loan portfolio | Originated | Total commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	217	297
Commercial loan portfolio | Originated | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	592,289	566,726
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	577,693	557,040
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,933	6,108
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,663	3,578
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	1,955,837	2,137,897
Commercial loan portfolio | Acquired | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,792,183	1,953,081
Commercial loan portfolio | Acquired | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	105,855	118,598
Commercial loan portfolio | Acquired | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,777	66,191
Commercial loan portfolio | Acquired | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	22	27
Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	625,640	715,481
Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	570,164	655,883
Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,067	36,809
Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,398	22,773
Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	16
Commercial loan portfolio | Acquired | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,299,896	1,391,930
Commercial loan portfolio | Acquired | Total commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,192,845	1,267,950
Commercial loan portfolio | Acquired | Total commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	72,729	81,692
Commercial loan portfolio | Acquired | Total commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,311	42,277
Commercial loan portfolio | Acquired | Total commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	11
Commercial loan portfolio | Acquired | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total loans	30,301	30,486
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,174	29,248
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	59	97
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,068	1,141
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	1,536,956	1,513,532
Owner-occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,050,430	2,059,557
Owner-occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,536,956	1,513,532
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,456,316	1,430,948
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,550	32,056
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	48,927	50,286
Owner-occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	163	242
Owner-occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	513,474	546,025
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	477,378	500,072
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,522	28,909
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,563	17,033
Owner-occupied | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	11	11
Non-owner occupied | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,961,863	1,966,330
Non-owner occupied | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,736,320	2,785,020
Non-owner occupied | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,961,863	1,966,330
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,897,810	1,901,822
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,195	39,416
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,807	25,092
Non-owner occupied | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	51	0
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	774,457	818,690
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	703,703	740,900
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	52,006	52,546
Non-owner occupied | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,748	25,244
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	36,454	40,295
Vacant land | Commercial loan portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	48,419	67,510
Vacant land | Commercial loan portfolio | Originated | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,454	40,295
Vacant land | Commercial loan portfolio | Originated | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,756	36,499
Vacant land | Commercial loan portfolio | Originated | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	98	0
Vacant land | Commercial loan portfolio | Originated | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,597	3,741
Vacant land | Commercial loan portfolio | Originated | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	55
Vacant land | Commercial loan portfolio | Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,965	27,215
Vacant land | Commercial loan portfolio | Acquired | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,764	26,978
Vacant land | Commercial loan portfolio | Acquired | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	201	237
Vacant land | Commercial loan portfolio | Acquired | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Vacant land | Commercial loan portfolio | Acquired | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0