Non-Covered Loans and Allowance for Non-Covered Loan Losses - Aging (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	$ 6,384,660	$ 6,273,669
Noncovered
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	20,058	16,563
Current Loans	6,337,937	6,219,902
Total loans	6,384,660	6,273,669
Accruing Loans Past Due 90 Days or More	688	640
Noncovered | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	9,664	6,513
Noncovered | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	5,065	1,723
Noncovered | Financing Receivables, Equal to Greater than 90 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	5,329	8,327
Noncovered | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	26,665	37,204
Noncovered | Secured
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	10,434	8,086
Current Loans	1,519,644	1,544,131
Total loans	1,535,133	1,558,316
Accruing Loans Past Due 90 Days or More		640
Noncovered | Secured | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	6,301	2,060
Noncovered | Secured | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,394	312
Noncovered | Secured | Financing Receivables, Equal to Greater than 90 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	2,739	5,714
Noncovered | Secured | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	5,055	6,099
Noncovered | Unsecured
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	457	642
Current Loans	119,841	122,247
Total loans	120,298	122,889
Noncovered | Unsecured | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	432	642
Noncovered | Unsecured | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	25
Noncovered | Secured by Commercial Properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	5,455	2,637
Current Loans	2,295,193	2,213,331
Total loans	2,317,410	2,235,643
Noncovered | Secured by Commercial Properties | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	428	442
Noncovered | Secured by Commercial Properties | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	3,206
Noncovered | Secured by Commercial Properties | Financing Receivables, Equal to Greater than 90 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,821	2,195
Noncovered | Secured by Commercial Properties | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	16,762	19,675
Noncovered | Secured by Residential Properties
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,940	3,198
Current Loans	819,217	762,818
Total loans	825,086	775,881
Accruing Loans Past Due 90 Days or More	688
Noncovered | Secured by Residential Properties | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,171	1,490
Noncovered | Secured by Residential Properties | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans		1,290
Noncovered | Secured by Residential Properties | Financing Receivables, Equal to Greater than 90 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	769	418
Noncovered | Secured by Residential Properties | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	3,929	9,865
Noncovered | Residential Construction Loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,054	315
Current Loans	208,601	176,937
Total loans	209,655	177,252
Noncovered | Residential Construction Loans | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	1,054	315
Noncovered | Commercial construction loans and land development
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	451	1,471
Current Loans	737,284	782,444
Total loans	738,654	785,353
Noncovered | Commercial construction loans and land development | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	51	1,370
Noncovered | Commercial construction loans and land development | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	400	101
Noncovered | Commercial construction loans and land development | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans	919	1,438
Noncovered | Consumer
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	267	214
Current Loans	37,995	40,105
Total loans	38,262	40,446
Noncovered | Consumer | Financing Receivables, 30 to 59 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	227	194
Noncovered | Consumer | Financing Receivables, 60 to 89 Days Past Due
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total Past Due Loans	40	20
Noncovered | Consumer | PCI loans
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Total loans		127
Noncovered | Broker-dealer
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Current Loans	600,162	577,889
Total loans	600,162	577,889
Noncovered | PrimeLending | U.S. Government Agencies
Non-Covered Loans and Allowance for Non-Covered Loan Losses
Accruing Loans Past Due 90 Days or More	73,400	84,500
Unpaid principal balance loans past due 90 days or more	$ 74,000	$ 85,200