Loans and Allowance for Credit Losses - Financing Receivables Past Due (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total past due	$ 65,440	$ 62,338
Current	20,331,413	19,725,538
Loans	20,396,853	19,787,876
30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	28,318	28,745
60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	15,401	12,333
90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	21,721	21,260
Commercial real estate- owner occupied
Financing Receivable, Past Due [Line Items]
Total past due	10,512	6,958
Current	2,639,658	2,662,808
Loans	2,650,170	2,669,766
Commercial real estate- owner occupied | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	5,892	2,307
Commercial real estate- owner occupied | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	2,157	2,932
Commercial real estate- owner occupied | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	2,463	1,719
Commercial real estate- Non-owner occupied
Financing Receivable, Past Due [Line Items]
Total past due	12,468	10,613
Current	5,058,104	5,028,839
Loans	5,070,572	5,039,452
Commercial real estate- Non-owner occupied | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	1,846	3,156
Commercial real estate- Non-owner occupied | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	5,917	3,641
Commercial real estate- Non-owner occupied | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	4,705	3,816
Consumer real estate – mortgage
Financing Receivable, Past Due [Line Items]
Total past due	21,811	21,107
Current	3,084,654	3,047,518
Loans	3,106,465	3,068,625
Consumer real estate – mortgage | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	10,673	11,646
Consumer real estate – mortgage | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	3,104	2,157
Consumer real estate – mortgage | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	8,034	7,304
Construction and land development
Financing Receivable, Past Due [Line Items]
Total past due	3,639	3,590
Current	2,517,298	2,426,893
Loans	2,520,937	2,430,483
Construction and land development | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	1,975	1,392
Construction and land development | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	137	711
Construction and land development | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	1,527	1,487
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total past due	15,406	17,316
Current	6,736,911	6,272,980
Loans	6,752,317	6,290,296
Commercial and industrial | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	6,873	8,474
Commercial and industrial | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	3,968	2,478
Commercial and industrial | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	4,565	6,364
Consumer and other
Financing Receivable, Past Due [Line Items]
Total past due	1,604	2,754
Current	294,788	286,500
Loans	296,392	289,254
Consumer and other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total past due	1,059	1,770
Consumer and other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total past due	118	414
Consumer and other | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total past due	$ 427	$ 570