Loans and Allowance for Loan Losses - Financing Receivables Past Due (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Loans		$ 19,345,642	$ 17,707,549
Nonaccrual loans	[1]	65,278	77,248
Currently performing impaired loans		33,500	52,500
Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		12,887	14,743
Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	7,985	10,586
Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		45,590	59,859
30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		43,140	58,301
90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		2,450	1,558
Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		19,213,902	17,545,113
Commercial real estate - mortgage
Financing Receivable, Past Due [Line Items]
Loans		7,709,245	7,164,954
Commercial real estate - mortgage | Owner-occupied
Financing Receivable, Past Due [Line Items]
Loans		2,595,837	2,653,433
Nonaccrual loans	[1]	11,011	16,025
Commercial real estate - mortgage | Owner-occupied | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		2,903	2,664
Commercial real estate - mortgage | Owner-occupied | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	897	874
Commercial real estate - mortgage | Owner-occupied | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		6,398	10,170
Commercial real estate - mortgage | Owner-occupied | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		6,398	10,170
Commercial real estate - mortgage | Owner-occupied | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		0	0
Commercial real estate - mortgage | Owner-occupied | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		2,574,628	2,623,700
Commercial real estate - mortgage | All other
Financing Receivable, Past Due [Line Items]
Loans		5,113,408	4,511,521
Nonaccrual loans	[1]	10,640	12,634
Commercial real estate - mortgage | All other | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		5,169	5,659
Commercial real estate - mortgage | All other | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	43	2,802
Commercial real estate - mortgage | All other | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		5,896	1,586
Commercial real estate - mortgage | All other | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		5,896	1,586
Commercial real estate - mortgage | All other | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		0	0
Commercial real estate - mortgage | All other | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		5,091,660	4,488,840
Consumer real estate - mortgage
Financing Receivable, Past Due [Line Items]
Loans		3,025,502	2,844,447
Nonaccrual loans	[1]	19,245	22,564
Consumer real estate - mortgage | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		3,216	3,689
Consumer real estate - mortgage | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	3,844	5,505
Consumer real estate - mortgage | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		9,824	18,059
Consumer real estate - mortgage | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		9,051	18,059
Consumer real estate - mortgage | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		773	0
Consumer real estate - mortgage | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		2,989,373	2,794,630
Construction and land development
Financing Receivable, Past Due [Line Items]
Loans		2,253,303	2,072,455
Nonaccrual loans	[1]	275	2,020
Construction and land development | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		1,274	2,108
Construction and land development | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	1,772	1,367
Construction and land development | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		2,005	3,759
Construction and land development | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		2,005	3,759
Construction and land development | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		0	0
Construction and land development | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		2,247,977	2,063,201
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans		5,891,038	5,271,421
Nonaccrual loans	[1]	23,931	23,022
Commercial and industrial | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		325	623
Commercial and industrial | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	1,429	38
Commercial and industrial | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		17,601	22,533
Commercial and industrial | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		16,524	21,451
Commercial and industrial | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		1,077	1,082
Commercial and industrial | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		5,847,752	5,225,205
Consumer and other
Financing Receivable, Past Due [Line Items]
Loans		466,554	354,272
Nonaccrual loans	[1]	176	983
Consumer and other | Purchased credit impaired, accruing
Financing Receivable, Past Due [Line Items]
Loans		0	0
Consumer and other | Purchased credit impaired, nonaccruing
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	[1]	0	0
Consumer and other | Past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		3,866	3,752
Consumer and other | 30-89 days past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		3,266	3,276
Consumer and other | 90 days or more past due and accruing
Financing Receivable, Past Due [Line Items]
Loans		600	476
Consumer and other | Current and Accruing
Financing Receivable, Past Due [Line Items]
Loans		$ 462,512	$ 349,537

[1] Approximately $33.5 million and $52.5 million of nonaccrual loans as of September 30, 2019 and December 31, 2018, respectively, were performing pursuant to their contractual terms at those dates.